# Linear equation solver

Discussion in 'General Electronics Chat' started by tindel, Mar 24, 2014.

1. ### tindel Thread Starter Active Member

Sep 16, 2012
576
196
Does anyone know of a free software that has a linear equation solver?

I use mathcad at work and it has a great linear equation solver that can solve a linear equation with variables... Unfortunately, I don't have the means to purchase mathcad for my home use. My ti89 will do it also but it's a bit cumbersome and I keep it at work too.

Any ideas?

Apr 5, 2008
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Jan 1, 2014
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4. ### Papabravo Expert

Feb 24, 2006
10,340
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MATLAB clone Scilab is free and will solve systems of linear equations.
R the statistical package is free and will find linear equationss to fit arbitrary data.

Nov 30, 2010
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6. ### russ_hensel Distinguished Member

Jan 11, 2009
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Checkout SageMath, you can use a free server or install. Just Google it.

7. ### tindel Thread Starter Active Member

Sep 16, 2012
576
196
Thanks for the tips...

I guess you get what you pay for in this scenario. What I'm trying to do is solve for nominal resistor values in a comparator circuit... I can do it by hand - no problem, but it's error prone. After solving for the resistor values then I want to determine the worst case of my comparator, given offset voltages and stuff like that.

This is super easy in Mathcad because in a solve block you can put in all of your input equations and it spits out the equations for R1, R2, and Rf without having to solve by hand (which is error prone - at least for me).

Any other suggestions. The real problem is that there is a 1Million different configurations for a comparator and I get tired of solving the equations for all of the resistors each time.

Actually, I was able to get pretty close to what I wanted by entering the following into the wolframalpha.com website pretty quickly... Took me a few minutes to figure out what the hell was going on at that website though, and then the lightbulb turned on.

1.235=2.5*(R23/(R1+R23)), 1.235=2*(R23/(R1+R23))+0.7*(R12/(R3+R12)), R12=R1*R2/(R1+R2), R23=R2*R3/(R2+R3), R1=100000

as you can see - this would be pretty time consuming to solve by hand... not impossible, but time consuming.
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Last edited: Mar 26, 2014
8. ### gootee Senior Member

Apr 24, 2007
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If you go to amazon.com and get the book, "Essential Mathcad", by Brent Maxfield, it comes with a license key for the full Mathcad software, which you can download, including several application add-ons. It's less than \$50.

9. ### tindel Thread Starter Active Member

Sep 16, 2012
576
196
Oooo... good tip gootee! I'll have to save my pennies! I wonder if you can get the license if you buy the book used... hrmmm.

10. ### gootee Senior Member

Apr 24, 2007
447
50
I would buy a new/unused copy. You probably would only be able to use the license from a used copy if the included license key had not ever been used by a previous owner.