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 JamesBond 15Oct2006 14:08

Multiplication of 2 Matrix in C

### Background

The output to the Matrix multiplication will be generated as follows.
Code:

```a11 a12 a13  A11 A12 A13  a11xA11+a12xA21+a13xA31 a11xA12+a12xA22+a13xA32 a21 a22 a23 x A21 A22 A23 = a21xA11+a22xA21+a23xA31 a21xA12+a22xA22+a23xA32 a31 a32 a33  A31 A32 A33  a31xA11+a32xA21+a33xA31```
More specific details are beyond the scope of this article but you can refer Matrix multiplication in wikipedia.

### The Code

Code: C

`void main(){    int m1[10][10],i,j,k,m2[10][10],add[10][10],mult[10][10],r1,c1,r2,c2;    printf("Enter number of rows and columns of first matrix MAX 10\n");    scanf("%d%d",&r1,&c1);    printf("Enter number of rows and columns of second matrix MAX 10\n");    scanf("%d%d",&r2,&c2);    if(r2==c1)    {        printf("Enter rows and columns of First matrix \n");        printf("Row wise\n");        for(i=0;i<r1;i++)        {            for(j=0;j<c1;j++)                scanf("%d",&m1[i][j]);        }        printf("You have entered the first matrix as follows:\n");        for(i=0;i<r1;i++)        {            for(j=0;j<c1;j++)                printf("%d\t",m1[i][j]);            printf("\n");        }        printf("Enter rows and columns of Second matrix \n");        printf("Again row wise\n");        for(i=0;i<r2;i++)        {            for(j=0;j<c2;j++)                scanf("%d",&m2[i][j]);        }        printf("You have entered the second matrix as follows:\n");        for(i=0;i<r2;i++)        {            for(j=0;j<c2;j++)                printf("%d\t",m2[i][j]);            printf("\n");        }        if(r1==r2&&c1==c2)        {            printf("Now we add both the above matrix \n");            printf("The result of the addition is as follows;\n");            for(i=0;i<r1;i++)            {                for(j=0;j<c1;j++)                {                    add[i][j]=m1[i][j]+m2[i][j];                    printf("%d\t",add[i][j]);                }                printf("\n");            }        }        else        {            printf("Addition cannot be done as rows or columns are not equal\n");        }        printf("Now we multiply both the above matrix \n");        printf("The result of the multiplication is as follows:\n");        /*a11xA11+a12xA21+a13xA31 a11xA12+a12xA22+a13xA32 a11xA13+a12xA23+a13xA33*/        for(i=0;i<r1;i++)        {            for(j=0;j<c2;j++)            {                mult[i][j]=0;                for(k=0;k<r1;k++)                {                    mult[i][j]+=m1[i][k]*m2[k][j];                    /*mult[0][0]=m1[0][0]*m2[0][0]+m1[0][1]*m2[1][0]+m1[0][2]*m2[2][0];*/                }                printf("%d\t",mult[i][j]);            }            printf("\n");        }        getch();    }    else    {        printf("Matrix multiplication cannot be done");    }}`

 elena 20May2007 18:05

Re: Multiplication of 2 Matrix in C

I'm a student and I've got to realize matrix multiplication using threads. I know how to do it without threads, but with threads it seems to me a little confusing, cause I haven't used threads.

Re: Multiplication of 2 Matrix in C

If you are user of Visual Studio (VC8) then you can easily use this

Code:

``` #include<omp.h> omp_set_num_threads(2 or 4 or 6) // as depends on your loop #pragma omp parallel for shared(mult, r1,c2) private(j,k)  for(i=0;i<r1;i++)         {             for(j=0;j<c2;j++)             {                 mult[i][j]=0;                 for(k=0;k<r1;k++)                 {                     mult[i][j]+=m1[i][k]*m2[k][j];                     /*mult[0][0]=m1[0][0]*m2[0][0]+m1[0][1]*m2[1][0]+m1[0][2]*m2[2][0];*/                 }               //printf("%d\t",mult[i][j]);             }             //printf("\n");         }```

By the use of OpenMP, parallel computing will be done. Today Google is using OpenMP, MPI, Grid Computing.

 wtfmate 21Jan2010 10:46

Re: Multiplication of 2 Matrix in C

Quote:
 Originally Posted by asadullah.ansari (Post 23455) If you are user of Visual Studio (VC8) then you can easily use this Code: ``` #include omp_set_num_threads(2 or 4 or 6) // as depends on your loop #pragma omp parallel for shared(mult, r1,c2) private(j,k)  for(i=0;i
There is a bug in this code; the inner most for loop should be:

for(k=0;k<r2;k++) { ... }

 mclark 23Mar2010 08:23

Re: Multiplication of 2 Matrix in C

I'm using xcode as my compiler, and it's stating that there are 2 bugs...
the first bug is on the second line where the "{" is. Xcode is says, "Return type of 'main' is not 'int'"... what does this mean?

and... the other bug is on the 72 line, where the getch() statement is.. xcode says, "Implicit declaration of function 'getch'"...

any idea of how to correct these two bugs?

 tajender 31Mar2010 11:00

Re: Multiplication of 2 Matrix in C

:nice::cuss:

 broncha 11Apr2010 01:30

Re: Multiplication of 2 Matrix in C

Quote:
 Originally Posted by mclark (Post 66099) I'm using xcode as my compiler, and it's stating that there are 2 bugs... the first bug is on the second line where the "{" is. Xcode is says, "Return type of 'main' is not 'int'"... what does this mean? and... the other bug is on the 72 line, where the getch() statement is.. xcode says, "Implicit declaration of function 'getch'"... any idea of how to correct these two bugs?
For the first bug change the data type of main from void to int . and at the end before closing main function "return 0"

Code:

`int main()`
for the second bug :
Are you including conio.h ?for getch() you should include conio.h

 3eenjohn 25Apr2010 00:32

Re: Multiplication of 2 Matrix in C

I have a very urgent Question ..... How to make a program which support brackets () and maths operations +-/* from user to input in a string ???
eg : [ (2+4) , 5*7 , ...... ]
and if any one knew the answer please thankfully could he send the program to my e-mail ( dodo-makram@hotmail.com )

 user2390 22Dec2010 12:37

Re: Multiplication of 2 Matrix in C

the above codes has one logical error in multiplying 2 matrices......
the correct portion of the codes:
for(i=0;i<r1;i++)
{
for(j=0;j<c2;j++)
{
mult[i][j]=0;
for(k=0;k<r1;k++)
{
....

 user2390 22Dec2010 12:37

Re: Multiplication of 2 Matrix in C

Excuse me ........
the correct portion is:
for(i=0;i<r1;i++)
{
for(j=0;j<c2;j++)
{
mult[i][j]=0;
for(k=0;k<c1;k++)
{
......

 gavinol 15Jan2011 21:01

Re: Multiplication of 2 Matrix in C

Only matrices of the same order (same number of rows and same number of columns) may be added by adding corresponding elements.

Example:

1. [2 -3] [7 3] [2 + 7 -3 + 3] [9 0]

[4 5] + [-2 7] = [4 + (-2) 5 + 7] = [2 12]

[6 0] [1 -5] [6 + 1 0 + (-5)] [7 -5]

2. [2 -3] [7 3 5]

[4 5] + [-2 7 -9]

[6 0] [1 -5 0]
The addition above is undefined since the two matrices do not have the same number of columns.

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