| Re: Feature with PV-WAVE routine INVERT [message #4611] |
Mon, 03 July 1995 00:00 |
thompson
Messages: 584
Registered: August 1991
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Senior Member |
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black@signal.dra.hmg.gb (John Black) writes:
> This is afollowup to amessage that I posted a few days ago, but it's expired
> here so I can't continue the thread.
> I've detected a feature with the PV-WAVE routine invert, which inverts a matrix.
> This routine has an optional parameter, status, which has the following states
> 0 = everything ok
> 1 = matrix was singular
> 2 = a small pivot element was used and it is likely that significant accuracy
> was lost (the routine uses Gaussian elimination)
> I looked at the value of status & for every example I tried status was set to 2
> However on doing
> PRINT, (INVERT(INVERT(matrix))-matrix)/matrix
> ie finding the fractional error, this turns out to be on the 10e-6 to 10e-7
> level. Status was always 2.
Just for the record, it appears that the INVERT function in IDL will give
STATUS=0 for well-behaved matrices.
Bill Thompson
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