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Re: Wrong results for "Large" simultaneous equation calculation
From: |
Ben Abbott |
Subject: |
Re: Wrong results for "Large" simultaneous equation calculation |
Date: |
Fri, 15 Jan 2010 19:20:47 -0500 |
On Jan 15, 2010, at 5:58 PM, David Parman wrote:
> I am new to Octave, and ran into a problem with my first real application. I
> am working with a large (120x120) set of simultaneous equations. When I solve
> the equations using the A\b nomenclature, I get an answer - no complaints
> from Octave. But the answer is clearly very wrong - all of the values are
> about 6 or more orders of magnitude smaller than they should be. I have the
> same set of calculations in MathCad, which yields an appropriate solution. I
> can also approximate the solution using direct analytical approach, which
> also confirms that the Octave result is way off.
>
> I found a couple of examples online for this type of solution (small 2x2 and
> 3x3 examples, one of which had the wrong answer on the webpage - confirmed by
> Octave and MathCad). These all worked just fine, but they have "nice" values
> (some of my values can be very large numbers, on the order of 10^18).
>
> I have spot checked the matrices and the values appear to be exactly the same
> in Octave as they are in MathCad. Does anybody have an idea what I might be
> missing here?
Unfortunately if you don't give us an example that doesn't work, no one will be
able to help.
Fortunately, you can easily provide your example :-)
If the matrix is only 120x120, try ...
save example.mat A b
... and attach example.mat to your reply.
Ben
Re: Wrong results for "Large" simultaneous equation calculation, Jaroslav Hajek, 2010/01/17