Read coefficients of linear equations from file and use jacobi method

This is a discussion on Read coefficients of linear equations from file and use jacobi method within the C++ Programming forums, part of the General Programming Boards category; hi; i did a function that get inputs of equation from user but i want to get from file Code: ...

  1. #1
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    Read coefficients of linear equations from file and use jacobi method

    hi;
    i did a function that get inputs of equation from user but i want to get from file


    Code:
    void getInput( int numUnKnowns, double** mat ){
        int i, j;
    
    
        printf
        (
    	"\nEnter values for the specified row and column below ...\n"
    	"(The last column is the value for the RHS of the equation.)\n"
        );
    
    
        for( i = 0 ; i < numUnKnowns ; i++ )
        {
    	mat[i] = (double*) malloc( (numUnKnowns+1)*sizeof(double) );
    	puts("");
    	for( j = 0 ; j < numUnKnowns+1 ; j++ )
    	{
    	    printf("matrix[%d][%d] : ", i, j);
    	    if( scanf("%lf", &mat[i][j]) != 1 )
    	    {
    		--j;
    		puts("Bad entry ... try again with a 'real' number.");
    	    }
    	    while( getchar() != '\n' ) ; /* flush stdin ... */
    	}
        }
    
    
        printf("\nThe matrix entered:\n\n");
        for( i = 0 ; i < numUnKnowns ; i++ )
        {
    	for( j = 0 ; j < numUnKnowns+1 ; j++ ) printf("%+9f ", mat[i][j]);
    	puts("");
        }
    
    
        printf("\nPress 'Enter' to start iteration ... ");
        getchar();
    }
    let file :
    7a - 2b + c + 2d = 3
    2a + 8b + 3c + d = -2
    -a + 5c + 2d = 5
    2b - c + 4d = 4

    can any one help me how function read from file.
    thanks

  2. #2
    Epy
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    Is this for a homework assignment or what? If it's for a homework assignment then fine, otherwise the Jacobi method is a waste of time. If you're going to use something that updates each value one by one then at least use Gauss-Seidel or Successive Over-relaxation (SOR).

    Looking at the system of equations you provided, I'm not sure the diagonal values are prominent enough to converge using any of those methods anyhow, you might need to use Gaussian elimination.

    Anyway, concerning your original question, you could make things much easier on yourself if you had a file like this:
    7 2 1 2 3
    2 8 3 1 -2
    -1 0 5 2 5
    0 2 -1 4 4

    Then you could use getline using a space as the delimiter to split those coefficients up into individual values, converting from string to a numerical type, of course.

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    Quote Originally Posted by Epy View Post
    Is this for a homework assignment or what? If it's for a homework assignment then fine, otherwise the Jacobi method is a waste of time. If you're going to use something that updates each value one by one then at least use Gauss-Seidel or Successive Over-relaxation (SOR).

    Looking at the system of equations you provided, I'm not sure the diagonal values are prominent enough to converge using any of those methods anyhow, you might need to use Gaussian elimination.

    Anyway, concerning your original question, you could make things much easier on yourself if you had a file like this:
    7 2 1 2 3
    2 8 3 1 -2
    -1 0 5 2 5
    0 2 -1 4 4

    Then you could use getline using a space as the delimiter to split those coefficients up into individual values, converting from string to a numerical type, of course.

    yes for a homework
    Gauss-Seidel or Successive Over-relaxation (SOR) are better than jacobi
    In homework assume for for strictly diagonally dominant matrices.
    just i want to read from file that have linear equations which are strictly diagonall

  4. #4
    C++まいる!Cをこわせ! Elysia's Avatar
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    This looks like C, not C++. Did you post it in the wrong section?
    Quote Originally Posted by Adak View Post
    io.h certainly IS included in some modern compilers. It is no longer part of the standard for C, but it is nevertheless, included in the very latest Pelles C versions.
    Quote Originally Posted by Salem View Post
    You mean it's included as a crutch to help ancient programmers limp along without them having to relearn too much.

    Outside of your DOS world, your header file is meaningless.

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    Quote Originally Posted by Elysia View Post
    This looks like C, not C++. Did you post it in the wrong section?
    yes in C
    thanks

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    and the hat of wrongness Salem's Avatar
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    If you dance barefoot on the broken glass of undefined behaviour, you've got to expect the occasional cut.
    If at first you don't succeed, try writing your phone number on the exam paper.
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