pointers array problem

[alfaceor]

Hi people.

This code works fine when N=DIM, but for N!=DIM doens't. How can i fix that and why this happen

#include <stdio.h>

void InitialValues(double *ptr_total_force,double *ptr_chain_r, double *ptr_chain_v, double sigma,const int N, const int DIM){

  double randomaux;
  for (int i=0;i<N;i++){
    for (int d=0;d<DIM;d++){
      // vector force
      ptr_total_force[i*N+d]=0;
      // vector positions and velocities
      ptr_chain_r[i*N+d] = 0.0;
      ptr_chain_v[i*N+d] = 0.0;
      if (d==0){
        randomaux = 0.001*i*d; //gsl_rng_uniform_pos(r1);
        ptr_chain_r[i*N+d] = randomaux;
        // vector velocities
        randomaux = 0.5*(i-d);//(2*gsl_ran_gaussian(r2,sigma) - 1);
        ptr_chain_v[i*N+d] = randomaux;
      }
    }
    ptr_chain_r[i*N+0] += sigma*i;
    printf("%f\t%f\n",ptr_chain_r[i*N+0],ptr_chain_v[i*N+0]);
  }

}


int main(){
  const int N=4;
  const int DIM=3;
  double total_force[N][DIM];
  double total_force_old[N][DIM];
  double chain_r[N][DIM];   // monomer positions
  double chain_v[N][DIM];   // monomer velocities
  double sigma = 1.0; // diametro
  
  InitialValues(total_force[0],chain_r[0], chain_v[0],sigma, N, DIM);
  printf("-------------\n");
  for (int i=0;i<N;i++){
    printf("%f\t%f\n",chain_r[i][0],chain_v[i][0]);
  }

}

OUTPUT examples
N=4, DIM=3
0.000000 0.000000
1.000000 0.500000
2.000000 1.000000
3.000000 1.500000
-------------
1.500000 0.000000
0.000000 0.000000
0.000000 0.000000
0.000000 0.000000

N=4, DIM=4
0.000000 0.000000
1.000000 0.500000
2.000000 1.000000
3.000000 1.500000
-------------
0.000000 0.000000
1.000000 0.500000
2.000000 1.000000
3.000000 1.500000


Pleaseeee any HELPPPP!!!

Carlos

[histrungalot]

Because data is stored in row-major order http://en.wikipedia.org/wiki/Row-major_order
Need to use i*DIM not i*N.

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#include <stdio.h> void InitialValues(double *ptr_total_force,double *ptr_chain_r, double *ptr_chain_v, double sigma,const int N, const int DI M){ double randomaux; for (int i=0;i<N;i++){ for (int d=0;d<DIM;d++){ // vector force ptr_total_force[i*DIM+d]=0; // vector positions and velocities ptr_chain_r[i*DIM+d] = 0.0; ptr_chain_v[i*DIM+d] = 0.0; if (d==0){ randomaux = 0.001*i*d; //gsl_rng_uniform_pos(r1); ptr_chain_r[i*DIM+d] = randomaux; // vector velocities randomaux = 0.5*(i-d);//(2*gsl_ran_gaussian(r2,sigma) - 1); ptr_chain_v[i*DIM+d] = randomaux; } } ptr_chain_r[i*DIM+0] += sigma*i; printf("%f\t%f\n",ptr_chain_r[i*DIM+0],ptr_chain_v[i*DIM+0]); } } int main(){ const int N=4; const int DIM=3; double total_force[N][DIM]; double total_force_old[N][DIM]; double chain_r[N][DIM]; // monomer positions double chain_v[N][DIM]; // monomer velocities double sigma = 1.0; // diametro InitialValues(total_force[0],chain_r[0], chain_v[0],sigma, N, DIM); printf("-------------\n"); for (int i=0;i<N;i++){ printf("%f\t%f\n",chain_r[i][0],chain_v[i][0]); } }

0.000000 0.000000 1.000000 0.500000 2.000000 1.000000 3.000000 1.500000 ------------- 0.000000 0.000000 1.000000 0.500000 2.000000 1.000000 3.000000 1.500000

[alfaceor]

thanks a lot histrungalot, maybe you know too how to debug the values of the pointer for example *ptr_chain_r ? because i need to debug other function and i just get the first value.

Carlos

[histrungalot]

Post example