c++ - sum of double variables -

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i have problem tyring basic addition. don't understand why returned value j11 0 while a11*g11 , a12*g21 have finite values. know has variable types - likely. appreciated. here code:

#include <vector> #include <iostream> #include <fstream> #include <cmath> #include <cstdlib> #include <set>  using namespace std;  void simple()  { double g11,g12,g13,g21,g22,g23,g31,g32; double g33,g41,g42,g43,g51,g52,g53,g61; double g62,g63,g71,g72,g73,g81,g82,g83; double j11; double xx,yy,zz; double a11,a12; vector<double> xcoor; vector<double> ycoor; vector<double> zcoor; double g1=1/sqrt(3); double g2=-1/sqrt(3);      xcoor.push_back(g1);     xcoor.push_back(g2);     xcoor.push_back(g1);     xcoor.push_back(g2);     xcoor.push_back(g1);     xcoor.push_back(g2);     xcoor.push_back(g1);     xcoor.push_back(g2);      ycoor.push_back(g1);     ycoor.push_back(g2);     ycoor.push_back(g2);     ycoor.push_back(g1);     ycoor.push_back(g1);     ycoor.push_back(g2);     ycoor.push_back(g2);     ycoor.push_back(g1);      zcoor.push_back(g2);     zcoor.push_back(g2);     zcoor.push_back(g2);     zcoor.push_back(g2);     zcoor.push_back(g1);     zcoor.push_back(g1);     zcoor.push_back(g1);     zcoor.push_back(g1);       (size_t z = 0 ; z < 43 ; z++) {         (size_t y = 0 ; y < 43 ; y++) {             (size_t x = 0 ; x < 43 ; x++) {                                           g11=x;                 g12=y;                 g13=z;                 g21=x;                 g22=y+1.;                 g23=z;                 g31=x+1.;                 g32=y+1.;                 g33=z;                 g41=x+1.;                 g42=y;                 g43=z;                 g51=x;                 g52=y;                 g53=z+1.;                 g61=x;                 g62=y+1.;                 g63=z+1.;                 g71=x+1.;                 g72=y+1.;                 g73=z+1.;                 g81=x+1.;                 g82=y;                 g83=z+1.;              for(size_t t = 0 ; t < 8 ; t++){                   xx = xcoor[t];                  yy = ycoor[t];                  zz = zcoor[t];                  a11=(-1./8.)*(1-yy)*(1-zz);                          a12=(1./8.)*(1-yy)*(1-zz);                  j11 = a11 * g11 + a12 * g21;                  cout<<j11<<endl;                  }             }         }     } }    int main () {      simple();     cout << "computation done." << endl;      return 0; }

this has zero:

j11 = a11 * g11 + a12 * g21;

because a11 = -a12 can see here:

a11=(-1./8.)*(1-yy)*(1-zz);          a12=(1./8.)*(1-yy)*(1-zz);

and g11 = g21 because of:

g11 = x g21 = x

nevertheless have no idea trying accomplish code.


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