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