Begin forwarded message: Date: January 16, 2010 1:09:09 PM EST
Subject: Re: Wrong results for "Large" simultaneous equation calculation
Ben,
Attached is the file. Any advice you can give will be greatly appreciated.
On Fri, Jan 15, 2010 at 4:20 PM, Ben Abbott <address@hidden> wrote:
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?
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
"The cost of a thing is the amount of life which is required to be exchanged for it" -- Thoreau
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example.mat