Matrix Inverse Code(c, c++, fortran or tksolver)

Question

I need a code to determine the inverse of an nxn matrix A using row operations. I am having a ridiculous time writing this code. Anything helps, I am a grad student and havent taken a programming class in years. Thanks.

Assuming you have been asked to write the inverter (rather than just needing to use one from a library) the first question is: can you perform the inversion by hand? If so, try coding the procedure, and then tell us *where you get stuck*... — dmckee --- ex-moderator kitten, Nov 23 '10 at 19:41
the inversion needs to be coded for nxn matrices, hence the problem — user517851, Nov 23 '10 at 21:04
Not a problem - get a good library. You need not code it - unless that's the assignment. If that's true, get busy. — duffymo, Nov 23 '10 at 21:20

score 2 · Answer 1 · answered Nov 23 '10 at 18:45

2

You might not really want the inverse. If you're trying to solve a system of equations you'd be better off using LU decomposition.

You don't say what language you'd like to write this app in. Java has Apache Commons Math; Python has NumPy; FORTRAN has LinPack. Pick a language and use a library; don't write it yourself.

answered Nov 23 '10 at 18:45

duffymo

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Exactly, see http://www.johndcook.com/blog/2010/01/19/dont-invert-that-matrix/ for more. Though, given this is a homework question, he is probably asked for the inverse. – ustun Nov 23 '10 at 18:53

score 2 · Answer 2 · answered Mar 15 '12 at 17:42

  SUBROUTINE MATINV(A,N)
  DIMENSION A(N,N)
  DO 1 I=1,N
     Z=A(I,I)
     A(I,I)=1.0
     DO 2 J=1,N
2       A(I,J)=A(1,J)/Z
     DO 1 K=1,N
        IF (K-I) 3,1,3
3          Z=A(K,I)
        A(K,I)=0.0
        DO 4 J=1,N
4          A(K,J)=A(K,J)-Z*A(I,J)
1 CONTINUE
  RETURN
  END

ustun · Answer 3 · 2010-11-23T18:40:42.707

1

I suggest Scilab or MATLAB for matrix operations if you haven't taken a programming class in years.

If it is a one time calculation, look at WolframAlpha.

If using libraries is an option for C++, look at Armadillo.

edited Nov 23 '10 at 18:40

answered Nov 23 '10 at 18:32

ustun

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Ideally i would use mathematica but these are the only programs allowed for the code: c c++ fortran tksolver – user517851 Nov 23 '10 at 18:34

score 0 · Answer 4 · answered Nov 24 '10 at 05:35

0

Look at Numerical Recipies Online. The Fortran 77, Ansi C and Fortran 90 code is free and you can get pleanty of clues on how to best proceed.

answered Nov 24 '10 at 05:35

John Alexiou

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Matrix Inverse Code(c, c++, fortran or tksolver)

4 Answers4