using a pointer to pointers

[booly_joon]

Hi

I have been pulling my hair out trying to figure this out. Please help!!!

Here is my project description:

By using a pointer to pointers **A and **B and the function calloc()
allocate the memory for the 4x4 matrices A[][] and B[][].
By using the pointers *a and *b and the function malloc()
allocate the memory for the 4-dimensional vectors a[] and b[].
Read the components of a and A from the given input file matrix.dat
(which is in the public/final directory; you need to copy it into your directory).
The first line of the input file contains the components of a. The rows of
matrix A are the last four lines of the input file. Print the components
of a[] and A[][]. By calling the function pmatrix(A,B,a,b,n), n=4,
which you will construct, determine the components of the matrix B=1.5*A*A, and the
vector b=(A*a)+0.5*a. Print the components of the matrix B and the vector b in the main.
Free dinamically allocated memory.
.................................................. ..............................
Output should look like:

Vector a is:
a[] = -1.200 1.200 -2.000 -0.500
Matrix A is:
2.700 1.500 3.200 2.400
-3.200 0.700 -2.600 4.300
1.400 0.600 2.100 -1.800
1.500 1.700 -2.600 -0.700
Matrix B is:
..... ...... ...... ......
..... ...... ...... ......
..... ...... ...... ......
..... ...... ...... ......
Vector b is:
b[] = ..... ..... ..... .....

My codes and I am stuck.

//void prob3(double ***A, double ***B, double **a, double **b)
void prob3(void)
{
FILE *matrix;
int k;
double ***A, ***B, **a, **b;
matrix=fopen("matrix.dat", "r");

*A= (double**)malloc(sizeof(double*)*4);
*B= (double**)malloc(sizeof(double*)*4);
*a= (double*)malloc(sizeof(double)*4);
*b= (double*)malloc(sizeof(double)*4);

for(k=0; k<4; k++)
{
fscanf(matrix, "%lf %lf %lf %lf", &(*A)[k][0], &(*A)[k][1], &(*A)[k][2], &(*A)[k][3]);
}
for(k=0; k<4; k++)
{
fscanf(matrix, "%lf", &(*a)[k]);
}
matrix1(*A, *B, *a, *b, 4);


}

void problem3()
{
double **A, **B, *a, *b;
int row, col;

printf("\nMatrix B is:\n\n");
for(row=0; row<4; row++)
{
for(col=0; col<4; col++)
{
printf("%.3f ", B[row][col]);
}
}
printf("\nVector b is: \n\n");
printf("a[] = ");
for(col=0; col<4; col++)
{
printf("%.3f ", b[col]);
}
for(row=0; row<4; row++)
{
free(A[row]);
free(B[row]);
}

free(A);
free(B);
free(a);
free(b);
}

[tesuji]

Hi booly_joon,

there is something wrong with your conception of two dimensional arrays. I suggest you should start learning some pointer's basic. This http://pweb.netcom.com/~tjensen/ptr/pointers.pdf
is a very good introduction to pointers and http://www.codeproject.com/KB/cpp/arrayDinamic.aspx gives a good example on how-to-use two dimensional arrays.

krs,
tesu

[Ancient Dragon]

Here is how I would allocate A

const int maxelms = 4;
int i;
double** A;
// allocate the first dimension
A = calloc(maxelms, sizeof(double *));
// now allocate each of the other dimensions
for(i = 0; i < maxelsms; ++i)
{
   A[i] = calloc(maxnums, sizeof(double));
}