How to multiply 3 arrays?

[Chris Winton]

I am trying to multiply three arrays together;
P_temp = A * A_t * P_k
Where the size or each array is [6][6].

Having difficulty in getting the correct answer. The method i am doing is;
A * A_t = a then using the result in a to use again in
P_temp = P_k * a

Any ideas how i could simplify this at all? Any help would be greatly appreciated!!

void prioriestimate (int a1[][3], int a2[][4], int a3[][4])
{
int T = 1;	
double A[6][6] =    {{1, 0, 0, T, 0, 0},
		     {0, 1, 0, 0, T, 0},
		     {0, 0, 1, 0, 0, T},
		     {0, 0, 0, 1, 0, 0},
		     {0, 0, 0, 0, 1, 0},
		     {0, 0, 0, 0, 0, 1}};
    
double A_t[6][6] =  {{1, 0, 0, 0, 0, 0},
		     {0, 1, 0, 0, 0, 0},
		     {0, 0, 1, 0, 0, 0},
		     {T, 0, 0, 1, 0, 0},
		     {0, T, 0, 0, 1, 0},
		     {0, 0, T, 0, 1, 0}};
 
double P_k[6][6] =  {{1, 0, 0, 0, 0, 0},
		     {0, 1, 0, 0, 0, 0},
		     {0, 0, 1, 0, 0, 0},
		     {0, 0, 0, 1, 0, 0},
		     {0, 0, 0, 0, 1, 0},
		     {0, 0, 0, 0, 1, 0}}; 


{

 int i = 0;

 int j = 0;

 int k = 0;
 int a;
        for(i = 0; i < 2; i++) 

           for( j = 0; j < 4; j++)

               for( k = 0; k < 3; k++)  

                   a[6][6] +=  A[6][6] * A_k[6][6];

}
{

 int i = 0;

 int j = 0;

 int k = 0;
 	for(i = 0; i < 2; i++) 

           for( j = 0; j < 4; j++)

               for( k = 0; k < 3; k++)  

                   P_temp[6][6] +=  a[6][6] * P_t[6][6];

}
}

[horace1]

to multiply c=a*b c[i][j] is evaluated

 c[i][j] = c[i][j] + a[i][k] * b[k][j]

[Chris Winton]

So instead of the line a[6][6] += A[6][6] * A_k[6][6];

I can just put P_temp[i][j] = P_k[i][j] + A_t[i][k] * A[k][j]?

[horace1]

I think more likly

a[i][j]] += A[i][k] * A_k[k][j];

make sure a[][] is zeroed first though

[vivek nandan]

you can also try this:
1.define a function that multiply two matrices and return result matrices.
2. Then pass the matrices in the given order . pass the two and get result. Then pass the third and the result.
3. You will have to use pointers to do this.

I have code that can multiply two matrices of any order matrix ,order given by the user , and return the result matrix. If you want , ask me.

[Chris Winton]

cheers vivek if you could send me the matrix code that would be great!!

[vivek nandan]

Here below is a generalized matrix multiplication code. You can multiply any two matrices of any order.The code is simple and you can easily figure out how to multiply n number of matrices of any order. Dont forget to say thanks :)

 
//Generalised matrix multilication and addition program

/*Author:Vivek nandan*/

#include <stdio.h>

#include <stdlib.h>

#define min(x1,x2) (x1>x2)?x2:x1

#define max(x1,x2) (x1>x2)?x1:x2

void add_mat(float*,float*,float*,int,int);

void mul_mat(float*,float*,float *,int,int,int,int);

void get_mat(float *,int,int);

int main(void)

{

static float *mat1,*mat2,*mat3;

static int row1,col1,row2,col2;int ch,k;

int i,j;

k=0;

printf("\n***********Matrix A*********************\n");

printf("\nEnter no of rows->");

scanf("%d",&row1);

printf("\nEnter no. of col->");

scanf("%d",&col1);

mat1=(float *)malloc(row1*col1*sizeof(float));

printf("\n************** Enter Matrx A data*******************\n");

get_mat(mat1,row1,col1);

printf("\n***********Matrix B*********************\n");

printf("\nEnter no of rows->");

scanf("%d",&row2);

printf("\nEnter no. of col->");

scanf("%d",&col2);

mat2=(float*)malloc(row2*col2*sizeof(float));

printf("\n************** Enter Matrx B data*******************\n");

get_mat(mat2,row2,col2);

printf("\nEnter Choice: \n");

printf("\n(1)Adding the matrices\n");

printf("\n(2)Multiplying matrices\n");

scanf("%d",&ch);

switch(ch)

{

case 1:

if((row1==row2)&&(col1==col2)){

mat3=(float*)malloc(row1*col1*sizeof(float));

add_mat(mat1,mat2,mat3,row1,col1);

printf("\n****Result of addition***********\n"); 

for(i=0;i<row1;i++)

{

  for(j=0;j<col1;j++)

        { printf("%f\t",*(mat3+k)); k++; }

printf("\n");

}

}

else{printf("\n<<<<<<<<Error!matrix cannot be added>>>>>>>>>>>>>>>\n");}

break;



case 2:

if(row2==col1){

mat3=(float*)malloc(row1*col2*sizeof(float));

mul_mat(mat1,mat2,mat3,row1,row2,col1,col2);

printf("\n<<<<<<<<<<<<Multiplication result>>>>>>>>>>>\n");

for(i=0;i<row1;i++)

{

  for(j=0;j<col2;j++)

        { printf("%f\t",*(mat3+k)); k++; }

printf("\n");

}

}

else{printf("\nERROR! Cannot be Multipied\n");}

break;



default:

printf("\n*******Nothing to be done!***********\n");

break;

};

system("PAUSE");

return 0;

}

void get_mat(float *x,int r,int c)

{

int i,j,k;

k=0;

for(i=0;i<r;i++)

{printf("\n........row=%d,col=%d.............\n",i,j);



for(j=0;j<c;j++)

  {scanf("%f",(x+k));

k++;

  }

}

printf("\n<<<<<Matrix entered>>>>>>>>>>>>\n");

k=0;

for(i=0;i<r;i++)

{//printf("\n........row=%d,col=%d.............\n",i,j);

for(j=0;j<c;j++)

  {printf("%f\t",*(x+k));

k++;

  }

printf("\n");

}



}
/* Matrix Addition Function */

void add_mat(float *x,float *y,float *z,int r,int c)

{

int i,j,k;

k=0;

for(i=0;i<r;i++)

{

  for(j=0;j<c;j++)

        { *(z+k)=*(x+k)+*(y+k);

             k++; }

}



}
/* Matrix Multiplication function */

void mul_mat(float *x,float *y,float * z,int r1,int c1,int r2,int c2) //mul_mat(*mat1,*mat2,*result,mat1_row,mat1_col,mat2_row,mat_col)

{

int i,j,k1,k2,k3;

float sum;

sum=0.00;

k1=k2=k3=0;

if(c1==r2)

 {

while(k3<r1*c2)

{

for(i=0;i<r1;i++){

                  for(j=0;j<r2;j++){

for(k1=0;k1<c2;k1++){

sum+=*(x+i*c1+k1)*(*(y+k1*c2+j)) ;

                     }

*(z+k3)=sum;

k3++;

sum=0;

}



}

}

}

else{printf("\nInside Error!\n");

    }



}

[Chris Winton]

Thank you very much!!!! helps alot