matrix inverstion code in C

[sheff]

HI everybody, I was trying to use the following code to invert a matrix, everytime I try to run this code, the only error msg that comes up is

'' inv030710.c:83: error: expected initializer before ‘int’ '' in this line of the code

void Gauss( RK8** a, RK8 ** b, int n)


int main()

{




I do not really understand the problem, can you please let me know how to sort out this probleml.

thank you alla nd looking forward to hearing from you.

# include <stdio.h>
#include<malloc.h>
#include<stdio.h>
#include<stdlib.h>
#include <time.h>
# include <string.h>
# include <math.h>
# define RK8 double 






void nrerror(char error_text[] )
  {

  fprintf(stderr,"Numerical Recipes run-time error...\n");
  fprintf(stderr,"%s\n",error_text);
  fprintf(stderr,"...now exiting to system...\n");
  exit(1);

  }

double *dvector( int nl,int nh)
  {

  double *v;

  v=(double *)malloc((unsigned) (nh-nl+1)*sizeof(double));
  if (!v) nrerror("allocation failure in dvector()");
  return v-nl;

  }


void free_dvector(double *v,int nl,int nh)
  {

  free((char*) (v+nl));
  nh++;

  }


double **dmatrix( int nrl, int nrh, int ncl, int nch )
  {

  int i;
  double **m;

  m=(double **) malloc((unsigned) (nrh-nrl+1)*sizeof(double*));
  if (!m) nrerror("allocation failure 1 in dmatrix()");
  m -= nrl;

  for(i=nrl;i<=nrh;i++) 
    {
    m[i]=(double *) malloc((unsigned) (nch-ncl+1)*sizeof(double));
    if (!m[i]) nrerror("allocation failure 2 in dmatrix()");
    m[i] -= ncl;
    }
  return m;

  }



void free_dmatrix( double **m, int nrl, int nrh, int ncl, int nch )
  {
  int i;

  for(i = nrh;i >= nrl; i--) free((char*) (m[i]+ncl));
  free((char*) (m+nrl));
  
  };


void Gauss( RK8** a, RK8 ** b,  int n)


int main()

{


double **first;
first = dmatrix( 0, 2, 0, 2 );

double **second;
second = dmatrix( 0, 2, 0, 2 );


 first[3][3]={{1.,2.,6.},{3.,4., 5.},{3.,4.,7.}};

second[3][3]={{0.,0.,0.},{0.,0., 0.},{0.,0.,0.}};

Gauss( first , second , 3);


}

void Gauss (RK8 ** a, RK8 ** b, int n)
{
  RK8 d, temp = 0, c;
  int i, j, k, m, nn, *ipvt;

  if ((ipvt = (int *) malloc (n * sizeof (int))) == NULL)
      memflt ();

  nn = n;
  for (i = 0; i < nn; i++)
    ipvt[i] = i;

  for (k = 0; k < nn; k++)
    {
      temp = 0.;
      m = k;
      for (i = k; i < nn; i++)
        {
          d = a[k][i];
          if (fabs (d) > temp)
            {
              temp = fabs (d);
              m = i;
            }
        }
      if (m != k)
        {
          j = ipvt[k];
          ipvt[k] = ipvt[m];
          ipvt[m] = j;
          for (j = 0; j < nn; j++)
            {
              temp = a[j][k];
              a[j][k] = a[j][m];
              a[j][m] = temp;
            }
        }
      d = 1 / a[k][k];
      for (j = 0; j < k; j++)
        {
          c = a[j][k] * d;
          for (i = 0; i < nn; i++)
            a[j][i] -= a[k][i] * c;
          a[j][k] = c;
        }
      for (j = k + 1; j < nn; j++)
        {
          c = a[j][k] * d;
          for (i = 0; i < nn; i++)
            a[j][i] -= a[k][i] * c;
          a[j][k] = c;
        }
      for (i = 0; i < nn; i++)
        a[k][i] = -a[k][i] * d;
      a[k][k] = d;
    }

  for (i = 0; i < nn; i++)
    memcpy (b[ipvt[i]], a[i], sizeof (RK8) * nn);

  free (ipvt);
}

[weaknessforcats]

This is bizarre code. It's not C because variables are defined in the middle of functions. It's not C++ because there are no C++ keywords in this code.

Variable names are reused. Nothing will compile using either C or C++ compiler.

I suggest using code that will compile.

[sheff]

hi weaknessforcats , thank u for your reply, I am really sure what you mean by bizarre code?

[weaknessforcats]

In main():

int main()

{


double **first;
first = dmatrix( 0, 2, 0, 2 );

double **second;
second = dmatrix( 0, 2, 0, 2 );

In C all variables need to be defined at the beginning of the function. You can't define second in the middle of the function.

first[3][3]={{1.,2.,6.},{3.,4., 5.},{3.,4.,7.}};

second[3][3]={{0.,0.,0.},{0.,0., 0.},{0.,0.,0.}};

Once a variable is defined, you can't reuse the name to define new arrays. This syntax: ]={{1.,2.,6.},{3 .,4., 5.},{3.,4.,7.}} is used to initialize a new array with values. The syntax doesnpt work of the variable is aleady defined. AND it was defined two lines up.

void Gauss( RK8** a, RK8 ** b, int n)


int main()

Function prototype missing a semi-colon.

If this was to be C++, there are no C++ headers being used:

# include <stdio.h>
#include<malloc.h>
#include<stdio.h>
#include<stdlib.h>
#include <time.h>
# include <string.h>
# include <math.h>

etc, etc...

[sheff]

HI weaknessforcats , THANK you very much for ur replies,

I just wanna direct your attention to the fact that we here first = dmatrix( 0, 2, 0, 2 );
we only tell the complier that our matrix '' first '' has got 3 rows and 3 columns ,

while in the following line we are identifying the values that are given to the matrix

first[3][3]={{1.,2.,6.},{3 .,4., 5.},{3.,4.,7.}} ;



I put the missing semi colum as you mentioned but ended up having more error msgs I aint got a clue what to do, I mean did u try to make the corrections you mentioned and see the result? can you do that and let me know if u r getting the right results plse,




{


double **first;
first = dmatrix( 0, 2, 0, 2 );

double **second;
second = dmatrix( 0, 2, 0, 2 );





first[3][3]={{1.,2.,6.},{3 .,4., 5.},{3.,4.,7.}} ;

second[3][3]={{0.,0.,0.},{0 .,0., 0.},{0.,0.,0.}} ;

Gauss( first , second , 3);


}

[Banfa]

In C all variables need to be defined at the beginning of the function. You can't define second in the middle of the function.

Erm, I think you can in C99

[weaknessforcats]

This code:

first[3][3]={{1.,2.,6.},{3.,4., 5.},{3.,4.,7.}};

creates a matrix named first as a two-dimensional 3x3 array with initial values.

You can only only use this syntx if the array does not already exist.

However, first is already defined as a double**. You can't use initializat syntax on an array that already exists.

You will need to individually initialize the array elements.