Thread: How to find inverse of a sparse matrix ?

  1. 06-24-2010 #1
    iamc
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    How to find inverse of a sparse matrix ?

    Hi,

    There are Numerical recipes (For C) functions namely ludcmp() and lubksb() to invert the matrix. I used them for a simple 3x3 matrix. I got the inverse. Then I mulitiplied that inverse with the original matrix. As expected I got the identity matrix.

    Now the same thing I tried for my 100x100 sparse matrix. I got the inverse. So to check, I multiplied this inverse by original matrix. But I did not get Identity matrix.

    Please tell efficient and correct way to invert a sparse matrix?

    Regards,
    iamc
  2. 06-25-2010 #2
    claudiu
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    Time to pick up the good ol' math book and remind yourself some matrix algebra.

    The inverse of an nxn matrix
    1. Get rid of gets(). Never ever ever use it again. Replace it with fgets() and use that instead.
    2. Get rid of void main and replace it with int main(void) and return 0 at the end of the function.
    3. Get rid of conio.h and other antiquated DOS crap headers.
    4. Don't cast the return value of malloc, even if you always always always make sure that stdlib.h is included.
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