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  • C++ C+中长表达式的优化+；

C++ C+中长表达式的优化+；

c++ optimization wolfram-mathematica

C++ C+中长表达式的优化+；,c++,optimization,wolfram-mathematica,C++,Optimization,Wolfram Mathematica,我有一个关于C/C++中长表达式的问题。因此，我计算了一个封闭形式的矩阵，我需要在我的代码。它是一个对称的6x6矩阵。所以基本上我想这样做 void calcMat(double * Mat, const double * S, const double * F, const double * tau, const double * D, const double * G) { //ReadIn all data from the given Arrays into const doubl

我有一个关于C/C++中长表达式的问题。因此，我计算了一个封闭形式的矩阵，我需要在我的代码。它是一个对称的6x6矩阵。所以基本上我想这样做

void calcMat(double * Mat, const double * S, const double * F, const double * tau, const double * D, const double * G)
{
   //ReadIn all data from the given Arrays into const double's
   const double G1 = G[0]; const double G2 = G[1]; const double G3 = G[2];

   const double F11 = F[0]; const double F12 = F[1]; const double F13 = F[2];
   const double F21 = F[3]; const double F22 = F[4]; const double F23 = F[5];
   const double F31 = F[6]; const double F32 = F[7]; const double F33 = F[8];

   const double sq2 = SQRT2 * 0.5;
   const double S11 = S[0]; const double S12 = sq2 * S[3]; const double S13 = sq2 * S[5];
   const double S22 = S[1]; const double S23 = sq2 * S[4];
   const double S33 = S[2];

   const double t11 = tau[0];
   const double t22 = tau[4];
   const double t33 = tau[8];
   const double t12 = tau[1];
   const double t23 = tau[5];
   const double t13 = tau[2];

   const double Sqr2I = 1. / sqrt(2.);
   const double D1111 = D[0]; const double D1122 = D[1]; const double D1133 = D[2]; const double D1112 = Sqr2I * D[3]; const double D1123 = Sqr2I * D[4]; const double D1113 = Sqr2I * D[5];
   const double D2222 = D[7]; const double D2233 = D[8]; const double D1222 = Sqr2I * D[9]; const double D2223 = Sqr2I*D[10]; const double D1322 = Sqr2I*D[11];
   const double D3333 = D[14]; const double D1233 = Sqr2I * D[15]; 
   const double D2333 = Sqr2I * D[16]; const double D1333 = Sqr2I * D[17];
   const double D1212 = 0.5 * D[21]; const double D1223 = 0.5 * D[22]; 
   const double D1213 = D[23];
   const double D2323 = 0.5 * D[28]; const double D1323 = 0.5 * D[29];
   const double D1313 = 0.5 * D[35];

   //Build Matrix first entry
   Mat[0] += (D1112*F11*G1*(F12*F12*S12*t11 + F13*F22*S13*t12 + F13*F32*S13*t13 + F11*S11*(F12*t11 + F22*t12 + F32*t13) +
     F12*(F13*S13*t11 + F21*S11*t12 + 2*F22*S12*t12 + F23*S13*t12 + F31*S11*t13 + 2*F32*S12*t13 + F33*S13*t13) + F21*F22*S11*t22 + F22*F22*S12*t22 + F22*F23*S13*t22 + F22*F31*S11*t23 +
     F21*F32*S11*t23 + 2*F22*F32*S12*t23 + F23*F32*S13*t23 + F22*F33*S13*t23 + F32*(F31*S11 + F32*S12 + F33*S13)*t33) +
  D1212*F12*G1*(F12*F12*S12*t11 + F13*F22*S13*t12 + F13*F32*S13*t13 + F11*S11*(F12*t11 + F22*t12 + F32*t13) +
     F12*(F13*S13*t11 + F21*S11*t12 + 2*F22*S12*t12 + F23*S13*t12 + F31*S11*t13 + 2*F32*S12*t13 + F33*S13*t13) + F21*F22*S11*t22 + F22*F22*S12*t22 + F22*F23*S13*t22 + F22*F31*S11*t23 +
     F21*F32*S11*t23 + 2*F22*F32*S12*t23 + F23*F32*S13*t23 + F22*F33*S13*t23 + F32*(F31*S11 + F32*S12 + F33*S13)*t33) +
  D1213*F13*G1*(F12*F12*S12*t11 + F13*F22*S13*t12 + F13*F32*S13*t13 + F11*S11*(F12*t11 + F22*t12 + F32*t13) +
     F12*(F13*S13*t11 + F21*S11*t12 + 2*F22*S12*t12 + F23*S13*t12 + F31*S11*t13 + 2*F32*S12*t13 + F33*S13*t13) + F21*F22*S11*t22 + F22*F22*S12*t22 + F22*F23*S13*t22 + F22*F31*S11*t23 +
     F21*F32*S11*t23 + 2*F22*F32*S12*t23 + F23*F32*S13*t23 + F22*F33*S13*t23 + F32*(F31*S11 + F32*S12 + F33*S13)*t33) +
  D1122*F11*G2*(F12*F12*S12*t11 + F13*F22*S13*t12 + F13*F32*S13*t13 + F11*S11*(F12*t11 + F22*t12 + F32*t13) +
     F12*(F13*S13*t11 + F21*S11*t12 + 2*F22*S12*t12 + F23*S13*t12 + F31*S11*t13 + 2*F32*S12*t13 + F33*S13*t13) + F21*F22*S11*t22 + F22*F22*S12*t22 + F22*F23*S13*t22 + F22*F31*S11*t23 +
     F21*F32*S11*t23 + 2*F22*F32*S12*t23 + F23*F32*S13*t23 + F22*F33*S13*t23 + F32*(F31*S11 + F32*S12 + F33*S13)*t33) +
  D1222*F12*G2*(F12*F12*S12*t11 + F13*F22*S13*t12 + F13*F32*S13*t13 + F11*S11*(F12*t11 + F22*t12 + F32*t13) +
     F12*(F13*S13*t11 + F21*S11*t12 + 2*F22*S12*t12 + F23*S13*t12 + F31*S11*t13 + 2*F32*S12*t13 + F33*S13*t13) + F21*F22*S11*t22 + F22*F22*S12*t22 + F22*F23*S13*t22 + F22*F31*S11*t23 +
     F21*F32*S11*t23 + 2*F22*F32*S12*t23 + F23*F32*S13*t23 + F22*F33*S13*t23 + F32*(F31*S11 + F32*S12 + F33*S13)*t33) +
  D1322*F13*G2*(F12*F12*S12*t11 + F13*F22*S13*t12 + F13*F32*S13*t13 + F11*S11*(F12*t11 + F22*t12 + F32*t13) +
     F12*(F13*S13*t11 + F21*S11*t12 + 2*F22*S12*t12 + F23*S13*t12 + F31*S11*t13 + 2*F32*S12*t13 + F33*S13*t13) + F21*F22*S11*t22 + F22*F22*S12*t22 + F22*F23*S13*t22 + F22*F31*S11*t23 +
     F21*F32*S11*t23 + 2*F22*F32*S12*t23 + F23*F32*S13*t23 + F22*F33*S13*t23 + F32*(F31*S11 + F32*S12 + F33*S13)*t33) +
  D1123*F11*G3*(F12*F12*S12*t11 + F13*F22*S13*t12 + F13*F32*S13*t13 + F11*S11*(F12*t11 + F22*t12 + F32*t13) +
     F12*(F13*S13*t11 + F21*S11*t12 + 2*F22*S12*t12 + F23*S13*t12 + F31*S11*t13 + 2*F32*S12*t13 + F33*S13*t13) + F21*F22*S11*t22 + F22*F22*S12*t22 + F22*F23*S13*t22 + F22*F31*S11*t23 +
     F21*F32*S11*t23 + 2*F22*F32*S12*t23 + F23*F32*S13*t23 + F22*F33*S13*t23 + F32*(F31*S11 + F32*S12 + F33*S13)*t33) +
  D1223*F12*G3*(F12*F12*S12*t11 + F13*F22*S13*t12 + F13*F32*S13*t13 + F11*S11*(F12*t11 + F22*t12 + F32*t13) +
     F12*(F13*S13*t11 + F21*S11*t12 + 2*F22*S12*t12 + F23*S13*t12 + F31*S11*t13 + 2*F32*S12*t13 + F33*S13*t13) + F21*F22*S11*t22 + F22*F22*S12*t22 + F22*F23*S13*t22 + F22*F31*S11*t23 +
     F21*F32*S11*t23 + 2*F22*F32*S12*t23 + F23*F32*S13*t23 + F22*F33*S13*t23 + F32*(F31*S11 + F32*S12 + F33*S13)*t33) +
  D1323*F13*G3*(F12*F12*S12*t11 + F13*F22*S13*t12 + F13*F32*S13*t13 + F11*S11*(F12*t11 + F22*t12 + F32*t13) +
     F12*(F13*S13*t11 + F21*S11*t12 + 2*F22*S12*t12 + F23*S13*t12 + F31*S11*t13 + 2*F32*S12*t13 + F33*S13*t13) + F21*F22*S11*t22 + F22*F22*S12*t22 + F22*F23*S13*t22 + F22*F31*S11*t23 +
     F21*F32*S11*t23 + 2*F22*F32*S12*t23 + F23*F32*S13*t23 + F22*F33*S13*t23 + F32*(F31*S11 + F32*S12 + F33*S13)*t33) +
  D1111*F11*G1*(F11*(F11*S11*t11 + F12*S12*t11 + F13*S13*t11 + F21*S11*t12 + F22*S12*t12 + F23*S13*t12 + F31*S11*t13 + F32*S12*t13 + F33*S13*t13) +
     F21*(F11*S11*t12 + F12*S12*t12 + F13*S13*t12 + F21*S11*t22 + F22*S12*t22 + F23*S13*t22 + F31*S11*t23 + F32*S12*t23 + F33*S13*t23) +
     F31*(F11*S11*t13 + F12*S12*t13 + F13*S13*t13 + F21*S11*t23 + F22*S12*t23 + F23*S13*t23 + F31*S11*t33 + F32*S12*t33 + F33*S13*t33)) +
  D1112*F12*G1*(F11*(F11*S11*t11 + F12*S12*t11 + F13*S13*t11 + F21*S11*t12 + F22*S12*t12 + F23*S13*t12 + F31*S11*t13 + F32*S12*t13 + F33*S13*t13) +
     F21*(F11*S11*t12 + F12*S12*t12 + F13*S13*t12 + F21*S11*t22 + F22*S12*t22 + F23*S13*t22 + F31*S11*t23 + F32*S12*t23 + F33*S13*t23) +
     F31*(F11*S11*t13 + F12*S12*t13 + F13*S13*t13 + F21*S11*t23 + F22*S12*t23 + F23*S13*t23 + F31*S11*t33 + F32*S12*t33 + F33*S13*t33)) +
  D1113*F13*G1*(F11*(F11*S11*t11 + F12*S12*t11 + F13*S13*t11 + F21*S11*t12 + F22*S12*t12 + F23*S13*t12 + F31*S11*t13 + F32*S12*t13 + F33*S13*t13) +
     F21*(F11*S11*t12 + F12*S12*t12 + F13*S13*t12 + F21*S11*t22 + F22*S12*t22 + F23*S13*t22 + F31*S11*t23 + F32*S12*t23 + F33*S13*t23) +
     F31*(F11*S11*t13 + F12*S12*t13 + F13*S13*t13 + F21*S11*t23 + F22*S12*t23 + F23*S13*t23 + F31*S11*t33 + F32*S12*t33 + F33*S13*t33)) +
  D1112*F11*G2*(F11*(F11*S11*t11 + F12*S12*t11 + F13*S13*t11 + F21*S11*t12 + F22*S12*t12 + F23*S13*t12 + F31*S11*t13 + F32*S12*t13 + F33*S13*t13) +
     F21*(F11*S11*t12 + F12*S12*t12 + F13*S13*t12 + F21*S11*t22 + F22*S12*t22 + F23*S13*t22 + F31*S11*t23 + F32*S12*t23 + F33*S13*t23) +
     F31*(F11*S11*t13 + F12*S12*t13 + F13*S13*t13 + F21*S11*t23 + F22*S12*t23 + F23*S13*t23 + F31*S11*t33 + F32*S12*t33 + F33*S13*t33)) +
  D1212*F12*G2*(F11*(F11*S11*t11 + F12*S12*t11 + F13*S13*t11 + F21*S11*t12 + F22*S12*t12 + F23*S13*t12 + F31*S11*t13 + F32*S12*t13 + F33*S13*t13) +
     F21*(F11*S11*t12 + F12*S12*t12 + F13*S13*t12 + F21*S11*t22 + F22*S12*t22 + F23*S13*t22 + F31*S11*t23 + F32*S12*t23 + F33*S13*t23) +
     F31*(F11*S11*t13 + F12*S12*t13 + F13*S13*t13 + F21*S11*t23 + F22*S12*t23 + F23*S13*t23 + F31*S11*t33 + F32*S12*t33 + F33*S13*t33)) +
  D1213*F13*G2*(F11*(F11*S11*t11 + F12*S12*t11 + F13*S13*t11 + F21*S11*t12 + F22*S12*t12 + F23*S13*t12 + F31*S11*t13 + F32*S12*t13 + F33*S13*t13) +
     F21*(F11*S11*t12 + F12*S12*t12 + F13*S13*t12 + F21*S11*t22 + F22*S12*t22 + F23*S13*t22 + F31*S11*t23 + F32*S12*t23 + F33*S13*t23) +
     F31*(F11*S11*t13 + F12*S12*t13 + F13*S13*t13 + F21*S11*t23 + F22*S12*t23 + F23*S13*t23 + F31*S11*t33 + F32*S12*t33 + F33*S13*t33)) +
  D1113*F11*G3*(F11*(F11*S11*t11 + F12*S12*t11 + F13*S13*t11 + F21*S11*t12 + F22*S12*t12 + F23*S13*t12 + F31*S11*t13 + F32*S12*t13 + F33*S13*t13) +
     F21*(F11*S11*t12 + F12*S12*t12 + F13*S13*t12 + F21*S11*t22 + F22*S12*t22 + F23*S13*t22 + F31*S11*t23 + F32*S12*t23 + F33*S13*t23) +
     F31*(F11*S11*t13 + F12*S12*t13 + F13*S13*t13 + F21*S11*t23 + F22*S12*t23 + F23*S13*t23 + F31*S11*t33 + F32*S12*t33 + F33*S13*t33)) +
  D1213*F12*G3*(F11*(F11*S11*t11 + F12*S12*t11 + F13*S13*t11 + F21*S11*t12 + F22*S12*t12 + F23*S13*t12 + F31*S11*t13 + F32*S12*t13 + F33*S13*t13) +
     F21*(F11*S11*t12 + F12*S12*t12 + F13*S13*t12 + F21*S11*t22 + F22*S12*t22 + F23*S13*t22 + F31*S11*t23 + F32*S12*t23 + F33*S13*t23) +
     F31*(F11*S11*t13 + F12*S12*t13 + F13*S13*t13 + F21*S11*t23 + F22*S12*t23 + F23*S13*t23 + F31*S11*t33 + F32*S12*t33 + F33*S13*t33)) +
  D1313*F13*G3*(F11*(F11*S11*t11 + F12*S12*t11 + F13*S13*t11 + F21*S11*t12 + F22*S12*t12 + F23*S13*t12 + F31*S11*t13 + F32*S12*t13 + F33*S13*t13) +
     F21*(F11*S11*t12 + F12*S12*t12 + F13*S13*t12 + F21*S11*t22 + F22*S12*t22 + F23*S13*t22 + F31*S11*t23 + F32*S12*t23 + F33*S13*t23) +
     F31*(F11*S11*t13 + F12*S12*t13 + F13*S13*t13 + F21*S11*t23 + F22*S12*t23 + F23*S13*t23 + F31*S11*t33 + F32*S12*t33 + F33*S13*t33)) +
  D1113*F11*G1*(F13*(F11*S11*t11 + F12*S12*t11 + F13*S13*t11 + F21*S11*t12 + F22*S12*t12 + F23*S13*t12 + F31*S11*t13 + F32*S12*t13 + F33*S13*t13) +
     F23*(F11*S11*t12 + F12*S12*t12 + F13*S13*t12 + F21*S11*t22 + F22*S12*t22 + F23*S13*t22 + F31*S11*t23 + F32*S12*t23 + F33*S13*t23) +
     F33*(F11*S11*t13 + F12*S12*t13 + F13*S13*t13 + F21*S11*t23 + F22*S12*t23 + F23*S13*t23 + F31*S11*t33 + F32*S12*t33 + F33*S13*t33)) +
  D1213*F12*G1*(F13*(F11*S11*t11 + F12*S12*t11 + F13*S13*t11 + F21*S11*t12 + F22*S12*t12 + F23*S13*t12 + F31*S11*t13 + F32*S12*t13 + F33*S13*t13) +
     F23*(F11*S11*t12 + F12*S12*t12 + F13*S13*t12 + F21*S11*t22 + F22*S12*t22 + F23*S13*t22 + F31*S11*t23 + F32*S12*t23 + F33*S13*t23) +
     F33*(F11*S11*t13 + F12*S12*t13 + F13*S13*t13 + F21*S11*t23 + F22*S12*t23 + F23*S13*t23 + F31*S11*t33 + F32*S12*t33 + F33*S13*t33)) +
  D1313*F13*G1*(F13*(F11*S11*t11 + F12*S12*t11 + F13*S13*t11 + F21*S11*t12 + F22*S12*t12 + F23*S13*t12 + F31*S11*t13 + F32*S12*t13 + F33*S13*t13) +
     F23*(F11*S11*t12 + F12*S12*t12 + F13*S13*t12 + F21*S11*t22 + F22*S12*t22 + F23*S13*t22 + F31*S11*t23 + F32*S12*t23 + F33*S13*t23) +
     F33*(F11*S11*t13 + F12*S12*t13 + F13*S13*t13 + F21*S11*t23 + F22*S12*t23 + F23*S13*t23 + F31*S11*t33 + F32*S12*t33 + F33*S13*t33)) +
  D1123*F11*G2*(F13*(F11*S11*t11 + F12*S12*t11 + F13*S13*t11 + F21*S11*t12 + F22*S12*t12 + F23*S13*t12 + F31*S11*t13 + F32*S12*t13 + F33*S13*t13) +
     F23*(F11*S11*t12 + F12*S12*t12 + F13*S13*t12 + F21*S11*t22 + F22*S12*t22 + F23*S13*t22 + F31*S11*t23 + F32*S12*t23 + F33*S13*t23) +
     F33*(F11*S11*t13 + F12*S12*t13 + F13*S13*t13 + F21*S11*t23 + F22*S12*t23 + F23*S13*t23 + F31*S11*t33 + F32*S12*t33 + F33*S13*t33)) +
  D1223*F12*G2*(F13*(F11*S11*t11 + F12*S12*t11 + F13*S13*t11 + F21*S11*t12 + F22*S12*t12 + F23*S13*t12 + F31*S11*t13 + F32*S12*t13 + F33*S13*t13) +
     F23*(F11*S11*t12 + F12*S12*t12 + F13*S13*t12 + F21*S11*t22 + F22*S12*t22 + F23*S13*t22 + F31*S11*t23 + F32*S12*t23 + F33*S13*t23) +
     F33*(F11*S11*t13 + F12*S12*t13 + F13*S13*t13 + F21*S11*t23 + F22*S12*t23 + F23*S13*t23 + F31*S11*t33 + F32*S12*t33 + F33*S13*t33)) +
  D1323*F13*G2*(F13*(F11*S11*t11 + F12*S12*t11 + F13*S13*t11 + F21*S11*t12 + F22*S12*t12 + F23*S13*t12 + F31*S11*t13 + F32*S12*t13 + F33*S13*t13) +
     F23*(F11*S11*t12 + F12*S12*t12 + F13*S13*t12 + F21*S11*t22 + F22*S12*t22 + F23*S13*t22 + F31*S11*t23 + F32*S12*t23 + F33*S13*t23) +
     F33*(F11*S11*t13 + F12*S12*t13 + F13*S13*t13 + F21*S11*t23 + F22*S12*t23 + F23*S13*t23 + F31*S11*t33 + F32*S12*t33 + F33*S13*t33)) +
  D1133*F11*G3*(F13*(F11*S11*t11 + F12*S12*t11 + F13*S13*t11 + F21*S11*t12 + F22*S12*t12 + F23*S13*t12 + F31*S11*t13 + F32*S12*t13 + F33*S13*t13) +
     F23*(F11*S11*t12 + F12*S12*t12 + F13*S13*t12 + F21*S11*t22 + F22*S12*t22 + F23*S13*t22 + F31*S11*t23 + F32*S12*t23 + F33*S13*t23) +
     F33*(F11*S11*t13 + F12*S12*t13 + F13*S13*t13 + F21*S11*t23 + F22*S12*t23 + F23*S13*t23 + F31*S11*t33 + F32*S12*t33 + F33*S13*t33)) +
  D1233*F12*G3*(F13*(F11*S11*t11 + F12*S12*t11 + F13*S13*t11 + F21*S11*t12 + F22*S12*t12 + F23*S13*t12 + F31*S11*t13 + F32*S12*t13 + F33*S13*t13) +
     F23*(F11*S11*t12 + F12*S12*t12 + F13*S13*t12 + F21*S11*t22 + F22*S12*t22 + F23*S13*t22 + F31*S11*t23 + F32*S12*t23 + F33*S13*t23) +
     F33*(F11*S11*t13 + F12*S12*t13 + F13*S13*t13 + F21*S11*t23 + F22*S12*t23 + F23*S13*t23 + F31*S11*t33 + F32*S12*t33 + F33*S13*t33)) +
  D1333*F13*G3*(F13*(F11*S11*t11 + F12*S12*t11 + F13*S13*t11 + F21*S11*t12 + F22*S12*t12 + F23*S13*t12 + F31*S11*t13 + F32*S12*t13 + F33*S13*t13) +
     F23*(F11*S11*t12 + F12*S12*t12 + F13*S13*t12 + F21*S11*t22 + F22*S12*t22 + F23*S13*t22 + F31*S11*t23 + F32*S12*t23 + F33*S13*t23) +
     F33*(F11*S11*t13 + F12*S12*t13 + F13*S13*t13 + F21*S11*t23 + F22*S12*t23 + F23*S13*t23 + F31*S11*t33 + F32*S12*t33 + F33*S13*t33)));
   //other terms in a similar fashion
}
我可以复制并粘贴所有+=计算，当我使用g++和-O0编译时，效果很好。但是，当我启用-O2时，编译需要非常长的时间，并且在某些机器上经常会耗尽内存。我的问题是：在它自己的范围内定义每个矩阵条目，然后添加，比如

void calcMat(double * Mat, other InputArrays)
{
   //ReadIn all data from the given Arrays into const double's
   //as shown above 
   //Build Matrix
   {
     const double Mat0 = (D1112*F11*G1*(F12*F12*S12*t11 + F13*F22*S13*t12 + F13*F32*S13*t13 + F11*S11*(F12*t11 + F22*t12 + F32*t13) +
     F12*(F13*S13*t11 + F21*S11*t12 + 2*F22*S12*t12 + F23*S13*t12 + F31*S11*t13 + 2*F32*S12*t13 + F33*S13*t13) + F21*F22*S11*t22 + F22*F22*S12*t22 + F22*F23*S13*t22 + F22*F31*S11*t23 +
     F21*F32*S11*t23 + 2*F22*F32*S12*t23 + F23*F32*S13*t23 + F22*F33*S13*t23 + F32*(F31*S11 + F32*S12 + F33*S13)*t33) +
  D1212*F12*G1*(F12*F12*S12*t11 + F13*F22*S13*t12 + F13*F32*S13*t13 + F11*S11*(F12*t11 + F22*t12 + F32*t13) +
     F12*(F13*S13*t11 + F21*S11*t12 + 2*F22*S12*t12 + F23*S13*t12 + F31*S11*t13 + 2*F32*S12*t13 + F33*S13*t13) + F21*F22*S11*t22 + F22*F22*S12*t22 + F22*F23*S13*t22 + F22*F31*S11*t23 +
     F21*F32*S11*t23 + 2*F22*F32*S12*t23 + F23*F32*S13*t23 + F22*F33*S13*t23 + F32*(F31*S11 + F32*S12 + F33*S13)*t33) +
  D1213*F13*G1*(F12*F12*S12*t11 + F13*F22*S13*t12 + F13*F32*S13*t13 + F11*S11*(F12*t11 + F22*t12 + F32*t13) +
     F12*(F13*S13*t11 + F21*S11*t12 + 2*F22*S12*t12 + F23*S13*t12 + F31*S11*t13 + 2*F32*S12*t13 + F33*S13*t13) + F21*F22*S11*t22 + F22*F22*S12*t22 + F22*F23*S13*t22 + F22*F31*S11*t23 +
     F21*F32*S11*t23 + 2*F22*F32*S12*t23 + F23*F32*S13*t23 + F22*F33*S13*t23 + F32*(F31*S11 + F32*S12 + F33*S13)*t33) +
  D1122*F11*G2*(F12*F12*S12*t11 + F13*F22*S13*t12 + F13*F32*S13*t13 + F11*S11*(F12*t11 + F22*t12 + F32*t13) +
     F12*(F13*S13*t11 + F21*S11*t12 + 2*F22*S12*t12 + F23*S13*t12 + F31*S11*t13 + 2*F32*S12*t13 + F33*S13*t13) + F21*F22*S11*t22 + F22*F22*S12*t22 + F22*F23*S13*t22 + F22*F31*S11*t23 +
     F21*F32*S11*t23 + 2*F22*F32*S12*t23 + F23*F32*S13*t23 + F22*F33*S13*t23 + F32*(F31*S11 + F32*S12 + F33*S13)*t33) +
  D1222*F12*G2*(F12*F12*S12*t11 + F13*F22*S13*t12 + F13*F32*S13*t13 + F11*S11*(F12*t11 + F22*t12 + F32*t13) +
     F12*(F13*S13*t11 + F21*S11*t12 + 2*F22*S12*t12 + F23*S13*t12 + F31*S11*t13 + 2*F32*S12*t13 + F33*S13*t13) + F21*F22*S11*t22 + F22*F22*S12*t22 + F22*F23*S13*t22 + F22*F31*S11*t23 +
     F21*F32*S11*t23 + 2*F22*F32*S12*t23 + F23*F32*S13*t23 + F22*F33*S13*t23 + F32*(F31*S11 + F32*S12 + F33*S13)*t33) +
  D1322*F13*G2*(F12*F12*S12*t11 + F13*F22*S13*t12 + F13*F32*S13*t13 + F11*S11*(F12*t11 + F22*t12 + F32*t13) +
     F12*(F13*S13*t11 + F21*S11*t12 + 2*F22*S12*t12 + F23*S13*t12 + F31*S11*t13 + 2*F32*S12*t13 + F33*S13*t13) + F21*F22*S11*t22 + F22*F22*S12*t22 + F22*F23*S13*t22 + F22*F31*S11*t23 +
     F21*F32*S11*t23 + 2*F22*F32*S12*t23 + F23*F32*S13*t23 + F22*F33*S13*t23 + F32*(F31*S11 + F32*S12 + F33*S13)*t33) +
  D1123*F11*G3*(F12*F12*S12*t11 + F13*F22*S13*t12 + F13*F32*S13*t13 + F11*S11*(F12*t11 + F22*t12 + F32*t13) +
     F12*(F13*S13*t11 + F21*S11*t12 + 2*F22*S12*t12 + F23*S13*t12 + F31*S11*t13 + 2*F32*S12*t13 + F33*S13*t13) + F21*F22*S11*t22 + F22*F22*S12*t22 + F22*F23*S13*t22 + F22*F31*S11*t23 +
     F21*F32*S11*t23 + 2*F22*F32*S12*t23 + F23*F32*S13*t23 + F22*F33*S13*t23 + F32*(F31*S11 + F32*S12 + F33*S13)*t33) +
  D1223*F12*G3*(F12*F12*S12*t11 + F13*F22*S13*t12 + F13*F32*S13*t13 + F11*S11*(F12*t11 + F22*t12 + F32*t13) +
     F12*(F13*S13*t11 + F21*S11*t12 + 2*F22*S12*t12 + F23*S13*t12 + F31*S11*t13 + 2*F32*S12*t13 + F33*S13*t13) + F21*F22*S11*t22 + F22*F22*S12*t22 + F22*F23*S13*t22 + F22*F31*S11*t23 +
     F21*F32*S11*t23 + 2*F22*F32*S12*t23 + F23*F32*S13*t23 + F22*F33*S13*t23 + F32*(F31*S11 + F32*S12 + F33*S13)*t33) +
  D1323*F13*G3*(F12*F12*S12*t11 + F13*F22*S13*t12 + F13*F32*S13*t13 + F11*S11*(F12*t11 + F22*t12 + F32*t13) +
     F12*(F13*S13*t11 + F21*S11*t12 + 2*F22*S12*t12 + F23*S13*t12 + F31*S11*t13 + 2*F32*S12*t13 + F33*S13*t13) + F21*F22*S11*t22 + F22*F22*S12*t22 + F22*F23*S13*t22 + F22*F31*S11*t23 +
     F21*F32*S11*t23 + 2*F22*F32*S12*t23 + F23*F32*S13*t23 + F22*F33*S13*t23 + F32*(F31*S11 + F32*S12 + F33*S13)*t33) +
  D1111*F11*G1*(F11*(F11*S11*t11 + F12*S12*t11 + F13*S13*t11 + F21*S11*t12 + F22*S12*t12 + F23*S13*t12 + F31*S11*t13 + F32*S12*t13 + F33*S13*t13) +
     F21*(F11*S11*t12 + F12*S12*t12 + F13*S13*t12 + F21*S11*t22 + F22*S12*t22 + F23*S13*t22 + F31*S11*t23 + F32*S12*t23 + F33*S13*t23) +
     F31*(F11*S11*t13 + F12*S12*t13 + F13*S13*t13 + F21*S11*t23 + F22*S12*t23 + F23*S13*t23 + F31*S11*t33 + F32*S12*t33 + F33*S13*t33)) +
  D1112*F12*G1*(F11*(F11*S11*t11 + F12*S12*t11 + F13*S13*t11 + F21*S11*t12 + F22*S12*t12 + F23*S13*t12 + F31*S11*t13 + F32*S12*t13 + F33*S13*t13) +
     F21*(F11*S11*t12 + F12*S12*t12 + F13*S13*t12 + F21*S11*t22 + F22*S12*t22 + F23*S13*t22 + F31*S11*t23 + F32*S12*t23 + F33*S13*t23) +
     F31*(F11*S11*t13 + F12*S12*t13 + F13*S13*t13 + F21*S11*t23 + F22*S12*t23 + F23*S13*t23 + F31*S11*t33 + F32*S12*t33 + F33*S13*t33)) +
  D1113*F13*G1*(F11*(F11*S11*t11 + F12*S12*t11 + F13*S13*t11 + F21*S11*t12 + F22*S12*t12 + F23*S13*t12 + F31*S11*t13 + F32*S12*t13 + F33*S13*t13) +
     F21*(F11*S11*t12 + F12*S12*t12 + F13*S13*t12 + F21*S11*t22 + F22*S12*t22 + F23*S13*t22 + F31*S11*t23 + F32*S12*t23 + F33*S13*t23) +
     F31*(F11*S11*t13 + F12*S12*t13 + F13*S13*t13 + F21*S11*t23 + F22*S12*t23 + F23*S13*t23 + F31*S11*t33 + F32*S12*t33 + F33*S13*t33)) +
  D1112*F11*G2*(F11*(F11*S11*t11 + F12*S12*t11 + F13*S13*t11 + F21*S11*t12 + F22*S12*t12 + F23*S13*t12 + F31*S11*t13 + F32*S12*t13 + F33*S13*t13) +
     F21*(F11*S11*t12 + F12*S12*t12 + F13*S13*t12 + F21*S11*t22 + F22*S12*t22 + F23*S13*t22 + F31*S11*t23 + F32*S12*t23 + F33*S13*t23) +
     F31*(F11*S11*t13 + F12*S12*t13 + F13*S13*t13 + F21*S11*t23 + F22*S12*t23 + F23*S13*t23 + F31*S11*t33 + F32*S12*t33 + F33*S13*t33)) +
  D1212*F12*G2*(F11*(F11*S11*t11 + F12*S12*t11 + F13*S13*t11 + F21*S11*t12 + F22*S12*t12 + F23*S13*t12 + F31*S11*t13 + F32*S12*t13 + F33*S13*t13) +
     F21*(F11*S11*t12 + F12*S12*t12 + F13*S13*t12 + F21*S11*t22 + F22*S12*t22 + F23*S13*t22 + F31*S11*t23 + F32*S12*t23 + F33*S13*t23) +
     F31*(F11*S11*t13 + F12*S12*t13 + F13*S13*t13 + F21*S11*t23 + F22*S12*t23 + F23*S13*t23 + F31*S11*t33 + F32*S12*t33 + F33*S13*t33)) +
  D1213*F13*G2*(F11*(F11*S11*t11 + F12*S12*t11 + F13*S13*t11 + F21*S11*t12 + F22*S12*t12 + F23*S13*t12 + F31*S11*t13 + F32*S12*t13 + F33*S13*t13) +
     F21*(F11*S11*t12 + F12*S12*t12 + F13*S13*t12 + F21*S11*t22 + F22*S12*t22 + F23*S13*t22 + F31*S11*t23 + F32*S12*t23 + F33*S13*t23) +
     F31*(F11*S11*t13 + F12*S12*t13 + F13*S13*t13 + F21*S11*t23 + F22*S12*t23 + F23*S13*t23 + F31*S11*t33 + F32*S12*t33 + F33*S13*t33)) +
  D1113*F11*G3*(F11*(F11*S11*t11 + F12*S12*t11 + F13*S13*t11 + F21*S11*t12 + F22*S12*t12 + F23*S13*t12 + F31*S11*t13 + F32*S12*t13 + F33*S13*t13) +
     F21*(F11*S11*t12 + F12*S12*t12 + F13*S13*t12 + F21*S11*t22 + F22*S12*t22 + F23*S13*t22 + F31*S11*t23 + F32*S12*t23 + F33*S13*t23) +
     F31*(F11*S11*t13 + F12*S12*t13 + F13*S13*t13 + F21*S11*t23 + F22*S12*t23 + F23*S13*t23 + F31*S11*t33 + F32*S12*t33 + F33*S13*t33)) +
  D1213*F12*G3*(F11*(F11*S11*t11 + F12*S12*t11 + F13*S13*t11 + F21*S11*t12 + F22*S12*t12 + F23*S13*t12 + F31*S11*t13 + F32*S12*t13 + F33*S13*t13) +
     F21*(F11*S11*t12 + F12*S12*t12 + F13*S13*t12 + F21*S11*t22 + F22*S12*t22 + F23*S13*t22 + F31*S11*t23 + F32*S12*t23 + F33*S13*t23) +
     F31*(F11*S11*t13 + F12*S12*t13 + F13*S13*t13 + F21*S11*t23 + F22*S12*t23 + F23*S13*t23 + F31*S11*t33 + F32*S12*t33 + F33*S13*t33)) +
  D1313*F13*G3*(F11*(F11*S11*t11 + F12*S12*t11 + F13*S13*t11 + F21*S11*t12 + F22*S12*t12 + F23*S13*t12 + F31*S11*t13 + F32*S12*t13 + F33*S13*t13) +
     F21*(F11*S11*t12 + F12*S12*t12 + F13*S13*t12 + F21*S11*t22 + F22*S12*t22 + F23*S13*t22 + F31*S11*t23 + F32*S12*t23 + F33*S13*t23) +
     F31*(F11*S11*t13 + F12*S12*t13 + F13*S13*t13 + F21*S11*t23 + F22*S12*t23 + F23*S13*t23 + F31*S11*t33 + F32*S12*t33 + F33*S13*t33)) +
  D1113*F11*G1*(F13*(F11*S11*t11 + F12*S12*t11 + F13*S13*t11 + F21*S11*t12 + F22*S12*t12 + F23*S13*t12 + F31*S11*t13 + F32*S12*t13 + F33*S13*t13) +
     F23*(F11*S11*t12 + F12*S12*t12 + F13*S13*t12 + F21*S11*t22 + F22*S12*t22 + F23*S13*t22 + F31*S11*t23 + F32*S12*t23 + F33*S13*t23) +
     F33*(F11*S11*t13 + F12*S12*t13 + F13*S13*t13 + F21*S11*t23 + F22*S12*t23 + F23*S13*t23 + F31*S11*t33 + F32*S12*t33 + F33*S13*t33)) +
  D1213*F12*G1*(F13*(F11*S11*t11 + F12*S12*t11 + F13*S13*t11 + F21*S11*t12 + F22*S12*t12 + F23*S13*t12 + F31*S11*t13 + F32*S12*t13 + F33*S13*t13) +
     F23*(F11*S11*t12 + F12*S12*t12 + F13*S13*t12 + F21*S11*t22 + F22*S12*t22 + F23*S13*t22 + F31*S11*t23 + F32*S12*t23 + F33*S13*t23) +
     F33*(F11*S11*t13 + F12*S12*t13 + F13*S13*t13 + F21*S11*t23 + F22*S12*t23 + F23*S13*t23 + F31*S11*t33 + F32*S12*t33 + F33*S13*t33)) +
  D1313*F13*G1*(F13*(F11*S11*t11 + F12*S12*t11 + F13*S13*t11 + F21*S11*t12 + F22*S12*t12 + F23*S13*t12 + F31*S11*t13 + F32*S12*t13 + F33*S13*t13) +
     F23*(F11*S11*t12 + F12*S12*t12 + F13*S13*t12 + F21*S11*t22 + F22*S12*t22 + F23*S13*t22 + F31*S11*t23 + F32*S12*t23 + F33*S13*t23) +
     F33*(F11*S11*t13 + F12*S12*t13 + F13*S13*t13 + F21*S11*t23 + F22*S12*t23 + F23*S13*t23 + F31*S11*t33 + F32*S12*t33 + F33*S13*t33)) +
  D1123*F11*G2*(F13*(F11*S11*t11 + F12*S12*t11 + F13*S13*t11 + F21*S11*t12 + F22*S12*t12 + F23*S13*t12 + F31*S11*t13 + F32*S12*t13 + F33*S13*t13) +
     F23*(F11*S11*t12 + F12*S12*t12 + F13*S13*t12 + F21*S11*t22 + F22*S12*t22 + F23*S13*t22 + F31*S11*t23 + F32*S12*t23 + F33*S13*t23) +
     F33*(F11*S11*t13 + F12*S12*t13 + F13*S13*t13 + F21*S11*t23 + F22*S12*t23 + F23*S13*t23 + F31*S11*t33 + F32*S12*t33 + F33*S13*t33)) +
  D1223*F12*G2*(F13*(F11*S11*t11 + F12*S12*t11 + F13*S13*t11 + F21*S11*t12 + F22*S12*t12 + F23*S13*t12 + F31*S11*t13 + F32*S12*t13 + F33*S13*t13) +
     F23*(F11*S11*t12 + F12*S12*t12 + F13*S13*t12 + F21*S11*t22 + F22*S12*t22 + F23*S13*t22 + F31*S11*t23 + F32*S12*t23 + F33*S13*t23) +
     F33*(F11*S11*t13 + F12*S12*t13 + F13*S13*t13 + F21*S11*t23 + F22*S12*t23 + F23*S13*t23 + F31*S11*t33 + F32*S12*t33 + F33*S13*t33)) +
  D1323*F13*G2*(F13*(F11*S11*t11 + F12*S12*t11 + F13*S13*t11 + F21*S11*t12 + F22*S12*t12 + F23*S13*t12 + F31*S11*t13 + F32*S12*t13 + F33*S13*t13) +
     F23*(F11*S11*t12 + F12*S12*t12 + F13*S13*t12 + F21*S11*t22 + F22*S12*t22 + F23*S13*t22 + F31*S11*t23 + F32*S12*t23 + F33*S13*t23) +
     F33*(F11*S11*t13 + F12*S12*t13 + F13*S13*t13 + F21*S11*t23 + F22*S12*t23 + F23*S13*t23 + F31*S11*t33 + F32*S12*t33 + F33*S13*t33)) +
  D1133*F11*G3*(F13*(F11*S11*t11 + F12*S12*t11 + F13*S13*t11 + F21*S11*t12 + F22*S12*t12 + F23*S13*t12 + F31*S11*t13 + F32*S12*t13 + F33*S13*t13) +
     F23*(F11*S11*t12 + F12*S12*t12 + F13*S13*t12 + F21*S11*t22 + F22*S12*t22 + F23*S13*t22 + F31*S11*t23 + F32*S12*t23 + F33*S13*t23) +
     F33*(F11*S11*t13 + F12*S12*t13 + F13*S13*t13 + F21*S11*t23 + F22*S12*t23 + F23*S13*t23 + F31*S11*t33 + F32*S12*t33 + F33*S13*t33)) +
  D1233*F12*G3*(F13*(F11*S11*t11 + F12*S12*t11 + F13*S13*t11 + F21*S11*t12 + F22*S12*t12 + F23*S13*t12 + F31*S11*t13 + F32*S12*t13 + F33*S13*t13) +
     F23*(F11*S11*t12 + F12*S12*t12 + F13*S13*t12 + F21*S11*t22 + F22*S12*t22 + F23*S13*t22 + F31*S11*t23 + F32*S12*t23 + F33*S13*t23) +
     F33*(F11*S11*t13 + F12*S12*t13 + F13*S13*t13 + F21*S11*t23 + F22*S12*t23 + F23*S13*t23 + F31*S11*t33 + F32*S12*t33 + F33*S13*t33)) +
  D1333*F13*G3*(F13*(F11*S11*t11 + F12*S12*t11 + F13*S13*t11 + F21*S11*t12 + F22*S12*t12 + F23*S13*t12 + F31*S11*t13 + F32*S12*t13 + F33*S13*t13) +
     F23*(F11*S11*t12 + F12*S12*t12 + F13*S13*t12 + F21*S11*t22 + F22*S12*t22 + F23*S13*t22 + F31*S11*t23 + F32*S12*t23 + F33*S13*t23) +
     F33*(F11*S11*t13 + F12*S12*t13 + F13*S13*t13 + F21*S11*t23 + F22*S12*t23 + F23*S13*t23 + F31*S11*t33 + F32*S12*t33 + F33*S13*t33)));
     Mat[0] += Mat0;
   } 
   ...
}
或者有没有其他方法可以帮助编译器解析大型表达式？

在结束之前，让我给您一个headstart

如果你只有你的表达式而没有算法，它是如何构造的，你仍然可以做一些优化。我用你的大表达式表示
Mat[0]
，并将其放入Mathematica中的一个变量中。我们用来优化常用表达式的函数如下

Experimental`OptimizeExpression[{x^2 Sin[x^2]}]
(*
Experimental`OptimizedExpression[
 Block[{Compile`$125}, 
  Compile`$125 = x^2; {Compile`$125 Sin[Compile`$125]}]]
*)
我们希望（a）使表达式更小，（b）使编译器更容易，因为它可能比大型表达式更好地优化语句

我们已经可以看到，优化的表达式（即使有所有新的临时变量）将比现在的表达式小6倍：

ByteCount[expr]
Experimental`OptimizeExpression[{expr}] // ByteCount

Out[560]= 64624

Out[561]= 11752
让我们尝试将优化后的表达式转换为C代码

<< CCodeGenerator`
opt = Experimental`OptimizeExpression[{expr}];
vars = # -> ToString[#] & /@ DeleteDuplicates[Cases[expr, _Symbol, Infinity]]
在这之后，我们有很多形式的东西

CDeclare["const double", CAssign["tmp55", "F22" "S12" "t23"]]
需要注意的是，操作（如这里的“F22”、“S12”和“t23”的乘法）仍然在那里。这些也需要被有效的c操作所取代

expr2 = expr1 //. {(h : (Times | Plus))[a__] :> COperator[h, {a}],
   Power[a_, b_] :> CCall["pow", {a, b}]}
现在，当结构正确时，您可以将其转换为可读的c代码

ToCCodeString @@ expr2
请注意，我还没有确认我所做的一切都是正确的。我甚至不会用这些替代品来实现它，但我只是尝试了一下，然后想，见鬼，我也可以发布它。创建的代码在本质上反映了Mathematica编译器也会做什么。也许这有助于：

const double tmp1 = pow(F12, 2);
const double tmp2 = S12 * t11 * tmp1;
const double tmp3 = F13 * F22 * S13 * t12;
const double tmp4 = F13 * F32 * S13 * t13;
const double tmp5 = F12 * t11;
const double tmp6 = F22 * t12;
const double tmp7 = F32 * t13;
const double tmp8 = tmp5 + tmp6 + tmp7;
const double tmp9 = F11 * S11 * tmp8;
const double tmp10 = F13 * S13 * t11;
const double tmp11 = F21 * S11 * t12;
const double tmp12 = 2 * F22 * S12 * t12;
const double tmp13 = F23 * S13 * t12;
const double tmp14 = F31 * S11 * t13;
const double tmp15 = 2 * F32 * S12 * t13;
const double tmp16 = F33 * S13 * t13;
const double tmp17 = tmp10 + tmp11 + tmp12 + tmp13 + tmp14 + tmp15 + tmp16;
const double tmp18 = F12 * tmp17;
const double tmp19 = F21 * F22 * S11 * t22;
const double tmp20 = pow(F22, 2);
const double tmp21 = S12 * t22 * tmp20;
const double tmp22 = F22 * F23 * S13 * t22;
const double tmp23 = F22 * F31 * S11 * t23;
const double tmp24 = F21 * F32 * S11 * t23;
const double tmp25 = 2 * F22 * F32 * S12 * t23;
const double tmp26 = F23 * F32 * S13 * t23;
const double tmp27 = F22 * F33 * S13 * t23;
const double tmp28 = F31 * S11;
const double tmp29 = F32 * S12;
const double tmp30 = F33 * S13;
const double tmp31 = tmp28 + tmp29 + tmp30;
const double tmp32 = F32 * t33 * tmp31;
const double tmp33 = tmp18 + tmp19 + tmp2 + tmp21 + tmp22 + tmp23 + tmp24 + tmp25 + tmp26 + tmp27 + tmp3 + tmp32 + tmp4 + tmp9;
const double tmp34 = F11 * S11 * t11;
const double tmp35 = F12 * S12 * t11;
const double tmp36 = F22 * S12 * t12;
const double tmp37 = F32 * S12 * t13;
const double tmp38 = tmp10 + tmp11 + tmp13 + tmp14 + tmp16 + tmp34 + tmp35 + tmp36 + tmp37;
const double tmp39 = F11 * tmp38;
const double tmp40 = F11 * S11 * t12;
const double tmp41 = F12 * S12 * t12;
const double tmp42 = F13 * S13 * t12;
const double tmp43 = F21 * S11 * t22;
const double tmp44 = F22 * S12 * t22;
const double tmp45 = F23 * S13 * t22;
const double tmp46 = F31 * S11 * t23;
const double tmp47 = F32 * S12 * t23;
const double tmp48 = F33 * S13 * t23;
const double tmp49 = tmp40 + tmp41 + tmp42 + tmp43 + tmp44 + tmp45 + tmp46 + tmp47 + tmp48;
const double tmp50 = F21 * tmp49;
const double tmp51 = F11 * S11 * t13;
const double tmp52 = F12 * S12 * t13;
const double tmp53 = F13 * S13 * t13;
const double tmp54 = F21 * S11 * t23;
const double tmp55 = F22 * S12 * t23;
const double tmp56 = F23 * S13 * t23;
const double tmp57 = F31 * S11 * t33;
const double tmp58 = F32 * S12 * t33;
const double tmp59 = F33 * S13 * t33;
const double tmp60 = tmp51 + tmp52 + tmp53 + tmp54 + tmp55 + tmp56 + tmp57 + tmp58 + tmp59;
const double tmp61 = F31 * tmp60;
const double tmp62 = tmp39 + tmp50 + tmp61;
const double tmp63 = F13 * tmp38;
const double tmp64 = F23 * tmp49;
const double tmp65 = F33 * tmp60;
const double tmp66 = tmp63 + tmp64 + tmp65;
Mat[0] = D1112 * F11 * G1 * tmp33 + D1212 * F12 * G1 * tmp33 + D1213 * F13 * G1 * tmp33 + D1122 * F11 * G2 * tmp33 + D1222 * F12 * G2 * tmp33 + D1322 * F13 * G2 * tmp33 + D1123 * F11 * G3 * tmp33 + D1223 * F12 * G3 * tmp33 + D1323 * F13 * G3 * tmp33 + D1111 * F11 * G1 * tmp62 + D1112 * F12 * G1 * tmp62 + D1113 * F13 * G1 * tmp62 + D1112 * F11 * G2 * tmp62 + D1212 * F12 * G2 * tmp62 + D1213 * F13 * G2 * tmp62 + D1113 * F11 * G3 * tmp62 + D1213 * F12 * G3 * tmp62 + D1313 * F13 * G3 * tmp62 + D1113 * F11 * G1 * tmp66 + D1213 * F12 * G1 * tmp66 + D1313 * F13 * G1 * tmp66 + D1123 * F11 * G2 * tmp66 + D1223 * F12 * G2 * tmp66 + D1323 * F13 * G2 * tmp66 + D1133 * F11 * G3 * tmp66 + D1233 * F12 * G3 * tmp66 + D1333 * F13 * G3 * tmp66;
在结束之前，让我给你一个开始

如果你只有你的表达式而没有算法，它是如何构造的，你仍然可以做一些优化。我用你的大表达式表示
Mat[0]
，并将其放入Mathematica中的一个变量中。我们用来优化常用表达式的函数如下

Experimental`OptimizeExpression[{x^2 Sin[x^2]}]
(*
Experimental`OptimizedExpression[
 Block[{Compile`$125}, 
  Compile`$125 = x^2; {Compile`$125 Sin[Compile`$125]}]]
*)
我们希望（a）使表达式更小，（b）使编译器更容易，因为它可能比大型表达式更好地优化语句

我们已经可以看到，优化的表达式（即使有所有新的临时变量）将比现在的表达式小6倍：

ByteCount[expr]
Experimental`OptimizeExpression[{expr}] // ByteCount

Out[560]= 64624

Out[561]= 11752
让我们尝试将优化后的表达式转换为C代码

<< CCodeGenerator`
opt = Experimental`OptimizeExpression[{expr}];
vars = # -> ToString[#] & /@ DeleteDuplicates[Cases[expr, _Symbol, Infinity]]
在这之后，我们有很多形式的东西

CDeclare["const double", CAssign["tmp55", "F22" "S12" "t23"]]
需要注意的是，操作（如这里的“F22”、“S12”和“t23”的乘法）仍然在那里。这些也需要被有效的c操作所取代

expr2 = expr1 //. {(h : (Times | Plus))[a__] :> COperator[h, {a}],
   Power[a_, b_] :> CCall["pow", {a, b}]}
现在，当结构正确时，您可以将其转换为可读的c代码

ToCCodeString @@ expr2
请注意，我还没有确认我所做的一切都是正确的。我甚至不会用这些替代品来实现它，但我只是尝试了一下，然后想，见鬼，我也可以发布它。创建的代码在本质上反映了Mathematica编译器也会做什么。也许这有助于：

const double tmp1 = pow(F12, 2);
const double tmp2 = S12 * t11 * tmp1;
const double tmp3 = F13 * F22 * S13 * t12;
const double tmp4 = F13 * F32 * S13 * t13;
const double tmp5 = F12 * t11;
const double tmp6 = F22 * t12;
const double tmp7 = F32 * t13;
const double tmp8 = tmp5 + tmp6 + tmp7;
const double tmp9 = F11 * S11 * tmp8;
const double tmp10 = F13 * S13 * t11;
const double tmp11 = F21 * S11 * t12;
const double tmp12 = 2 * F22 * S12 * t12;
const double tmp13 = F23 * S13 * t12;
const double tmp14 = F31 * S11 * t13;
const double tmp15 = 2 * F32 * S12 * t13;
const double tmp16 = F33 * S13 * t13;
const double tmp17 = tmp10 + tmp11 + tmp12 + tmp13 + tmp14 + tmp15 + tmp16;
const double tmp18 = F12 * tmp17;
const double tmp19 = F21 * F22 * S11 * t22;
const double tmp20 = pow(F22, 2);
const double tmp21 = S12 * t22 * tmp20;
const double tmp22 = F22 * F23 * S13 * t22;
const double tmp23 = F22 * F31 * S11 * t23;
const double tmp24 = F21 * F32 * S11 * t23;
const double tmp25 = 2 * F22 * F32 * S12 * t23;
const double tmp26 = F23 * F32 * S13 * t23;
const double tmp27 = F22 * F33 * S13 * t23;
const double tmp28 = F31 * S11;
const double tmp29 = F32 * S12;
const double tmp30 = F33 * S13;
const double tmp31 = tmp28 + tmp29 + tmp30;
const double tmp32 = F32 * t33 * tmp31;
const double tmp33 = tmp18 + tmp19 + tmp2 + tmp21 + tmp22 + tmp23 + tmp24 + tmp25 + tmp26 + tmp27 + tmp3 + tmp32 + tmp4 + tmp9;
const double tmp34 = F11 * S11 * t11;
const double tmp35 = F12 * S12 * t11;
const double tmp36 = F22 * S12 * t12;
const double tmp37 = F32 * S12 * t13;
const double tmp38 = tmp10 + tmp11 + tmp13 + tmp14 + tmp16 + tmp34 + tmp35 + tmp36 + tmp37;
const double tmp39 = F11 * tmp38;
const double tmp40 = F11 * S11 * t12;
const double tmp41 = F12 * S12 * t12;
const double tmp42 = F13 * S13 * t12;
const double tmp43 = F21 * S11 * t22;
const double tmp44 = F22 * S12 * t22;
const double tmp45 = F23 * S13 * t22;
const double tmp46 = F31 * S11 * t23;
const double tmp47 = F32 * S12 * t23;
const double tmp48 = F33 * S13 * t23;
const double tmp49 = tmp40 + tmp41 + tmp42 + tmp43 + tmp44 + tmp45 + tmp46 + tmp47 + tmp48;
const double tmp50 = F21 * tmp49;
const double tmp51 = F11 * S11 * t13;
const double tmp52 = F12 * S12 * t13;
const double tmp53 = F13 * S13 * t13;
const double tmp54 = F21 * S11 * t23;
const double tmp55 = F22 * S12 * t23;
const double tmp56 = F23 * S13 * t23;
const double tmp57 = F31 * S11 * t33;
const double tmp58 = F32 * S12 * t33;
const double tmp59 = F33 * S13 * t33;
const double tmp60 = tmp51 + tmp52 + tmp53 + tmp54 + tmp55 + tmp56 + tmp57 + tmp58 + tmp59;
const double tmp61 = F31 * tmp60;
const double tmp62 = tmp39 + tmp50 + tmp61;
const double tmp63 = F13 * tmp38;
const double tmp64 = F23 * tmp49;
const double tmp65 = F33 * tmp60;
const double tmp66 = tmp63 + tmp64 + tmp65;
Mat[0] = D1112 * F11 * G1 * tmp33 + D1212 * F12 * G1 * tmp33 + D1213 * F13 * G1 * tmp33 + D1122 * F11 * G2 * tmp33 + D1222 * F12 * G2 * tmp33 + D1322 * F13 * G2 * tmp33 + D1123 * F11 * G3 * tmp33 + D1223 * F12 * G3 * tmp33 + D1323 * F13 * G3 * tmp33 + D1111 * F11 * G1 * tmp62 + D1112 * F12 * G1 * tmp62 + D1113 * F13 * G1 * tmp62 + D1112 * F11 * G2 * tmp62 + D1212 * F12 * G2 * tmp62 + D1213 * F13 * G2 * tmp62 + D1113 * F11 * G3 * tmp62 + D1213 * F12 * G3 * tmp62 + D1313 * F13 * G3 * tmp62 + D1113 * F11 * G1 * tmp66 + D1213 * F12 * G1 * tmp66 + D1313 * F13 * G1 * tmp66 + D1123 * F11 * G2 * tmp66 + D1223 * F12 * G2 * tmp66 + D1323 * F13 * G2 * tmp66 + D1133 * F11 * G3 * tmp66 + D1233 * F12 * G3 * tmp66 + D1333 * F13 * G3 * tmp66;
不清楚你在问什么。请选择一种语言。如果-O2标志确实导致您在一个合理的现代系统上耗尽内存，那么您的源代码必须非常广泛。哦，天哪。你应该知道如何计算可读C++代码中的计算，而不是使用这个自动生成的混乱。我想我会回到Mathematica并要求它工作更努力，也许说服它消除常见的子表达式。例如，我看到像
F33*S13*t13
这样的术语反复出现，如果代码在大量语句之外计算这些术语一次，您可能能够帮助编译器。事实上，我看得越多，（a）我就越能看到此类术语的重复出现，（b）我就越目瞪口呆。不清楚你在问什么。请选择一种语言。如果-O2标志确实导致您在一个合理的现代系统上耗尽内存，那么您的源代码必须非常广泛。哦，天哪。你应该知道如何计算可读C++代码中的计算，而不是使用这个自动生成的混乱。我想我会回到Mathematica并要求它工作更努力，也许说服它消除常见的子表达式。例如，我看到像
F33*S13*t13
这样的术语反复出现，如果代码在大量语句之外计算这些术语一次，您可能能够帮助编译器。事实上，我看得越多，（a）我就越能看到这些术语的重复出现，（b）我就越容易发疯。