Comp4

Basic Matrix Operations¶

We will see how to use arrays for 1D, 2D matrices and then doing matrix operations.

In [1]:

%%writefile mat_unit.c
#include<stdio.h>
void main()
{
  // Write a unit matrix of given dimension
  int dim;
  printf("Enter the size of the matrix\n");
  scanf("%d",&dim);

	int a[dim][dim],i,j;
	for(i=0;i<dim;i++) {
		for(j=0;j<dim;j++) {
			if(i==j) a[i][j]=1;
			else     a[i][j]=0;
		}
	}
	for(i=0;i<dim;i++) {
		for(j=0;j<dim;j++) {
			printf("%d\t",a[i][j]);
		}
		printf("\n");
	}
}

Writing mat_unit.c

In [3]:

!gcc mat_unit.c
!./a.out

Enter the size of the matrix
2
1	0	
0	1	

In [ ]:

%%writefile mat_addition.c
#include<stdio.h>

int main() {
   int a[10][10], b[10][10], s[10][10], i, j,r,c;
   int sum = 0;
label:   printf("Enter the Number  of  Rows ");
   scanf("%d",&r);
   printf("Enter the Number  of  columns ");
   scanf("%d",&c);
   printf("\nEnter First Matrix : ");
   for (i = 0; i < r; i++) {
      for (j = 0; j < c ; j++) {
         scanf("%d", &a[i][j]);
      }
   }
   printf("\nEnter Second Matrix:");
   for (i = 0; i<r; i++) {
      for (j = 0; j<c; j++) {
         scanf("%d", &b[i][j]);
      }
   }
   printf("The First Matrix is: \n");
   for (i=0; i<r; i++) {
      for (j= 0; j<c; j++) {
         printf("%d ", a[i][j]);
       }
       printf("\n");
   }

   printf("The Second Matrix is : \n");
   for (i = 0; i<r; i++) {
      for (j = 0; j<c; j++) {
         printf(" %d ", b[i][j]);
      }
      printf("\n");
   }

   //Addition
   for (i=0; i<r; i++) {
      for (j=0; j<c; j++) s[i][j]= a[i][j]+b[i][j];
      }

   printf("\nAdition Of Two Matrices :\n");
   for (i=0;i<r;i++) {
      for (j= 0;j<c;j++) {
         printf("%d \t",s[i][j]);
      }
      printf("\n");
   }

   return (0);
}

Overwriting mat_addition.c

In [ ]:

!gcc mat_addition.c
!./a.out

Enter the Number  of  Rows 2
Enter the Number  of  columns 2

Enter First Matrix : 1 2 3
4

Enter Second Matrix:4 5 6 7
The First Matrix is: 
1 2 
3 4 
The Second Matrix is : 
 4  5 
 6  7 

 Adition Of Two Matrices : 
5 	7 	
9 	11 	

Passing arrays to functions¶

In the above example of matrix addition, if we want to avoid writing codes to print matrices several times, we may put them inside functions. But C copies in its arguments. For arrays, C copies in the address of the array. In C an array without using a pointer can not be passed. Arrays are always passed by pointer. The array label itself decays into a pointer to the first byte(element) automatically. Passing an array to a function allows the function to directly access and modify the original array.

So we will make use of pointer in the program. Stil, we have a limit of size of the matrix. We take sufficiently large matrix in the code for any future requirements of execution. Defining the size of a matrix during execution is only possible using advanced memory management, dynamic memory allocation concepts.

Here is a good web link for clear understanding.

In [45]:

%%writefile mat_mul.c
#include<stdio.h>

// Function to read a matrix using array notation
void readMatrix(int matrix[][10], int rows, int cols) {
    printf("Enter the elements of the matrix:\n");
    for (int i = 0; i < rows; i++) {
        for (int j = 0; j < cols; j++) {
            printf("Enter element at [%d][%d]: ", i, j);
            scanf("%d", &matrix[i][j]);
        }
    }
}

// Function to print the matrix (for verification)
void printMatrix(int matrix[][10], int rows, int cols) {
    printf("\nThe matrix is:\n");
    for (int i = 0; i < rows; i++) {
        for (int j = 0; j < cols; j++) {
            printf("%d\t", matrix[i][j]);
        }
        printf("\n");
    }
}

// Function for Matrix Multiplication
int multMatrix (int m1[][10], int r1, int c1, int m2[][10], int r2, int c2, int m3[][10]) {
    int sum;
    for (int i=0; i<=r1; i++) {
      for (int j=0; j<=c2; j++) {
         sum=0;
         for (int k=0; k<c1; k++) sum += m1[i][k]*m2[k][j];
         m3[i][j] = sum;
      }
    }
}

int main()
{
   int a[10][10], b[10][10], c[10][10], r1,r2,c1,c2;

label:   printf("Enter the Number of Rows of the First matrix:");
   scanf("%d",&r1);
   printf("Enter the Number  of  columns of the First matrix:");
   scanf("%d",&c1);

   // Call the function to read the matrix
   readMatrix(a, r1, c1);

   printf("Enter the Number  of  Rows of the second matrix:");
   scanf("%d",&r2);
   printf("Enter the Number  of  columns of the Second matrix:");
   scanf("%d",&c2);

   // Call the function to read the matrix
   readMatrix(b, r2, c2);

   if (c1!=r2) {
      printf("Matrix Multiplication not possible \n Enter correct dimension ");
      goto label;
	 }

   printf("The First Matrix is: \n");
   printMatrix(a, r1, c1);

   printf("The Second Matrix is : \n");
   printMatrix(b, r2, c2);

   printf("\n Multiplication Of Two Matrices : \n");
   multMatrix(a, r1, c1, b, r2, c2, c);
   printMatrix(c, r1, c2);

   return (0);
}

Overwriting mat_mul.c

In [44]:

!gcc mat_mul.c
!./a.out

Enter the Number of Rows of the First matrix:2
Enter the Number  of  columns of the First matrix:2
Enter the elements of the matrix:
Enter element at [0][0]: 1
Enter element at [0][1]: 2
Enter element at [1][0]: 3
Enter element at [1][1]: 4
Enter the Number  of  Rows of the second matrix:2
Enter the Number  of  columns of the Second matrix:2
Enter the elements of the matrix:
Enter element at [0][0]: 5
Enter element at [0][1]: 6
Enter element at [1][0]: 7
Enter element at [1][1]: 8
The First Matrix is: 

The matrix is:
1	2	
3	4	
The Second Matrix is : 

The matrix is:
5	6	
7	8	

 Multiplication Of Two Matrices : 

The matrix is:
19	22	
43	50