question 1

[midsidenode]

I apologize for this stupid question. I am by no means a whiz at MATLAB like those of you on this thread. I fumble thru it and after using the help documentation, I will usually get things to work out. But this time I am having no luck. I have created a script and it works just fine. It calculates the correct answer every time. The problem is that the answer is displayed with "alot" of digits (a whole number) in the numerator and "alot" of digits (another whole number) in the denominator. It appears as though is wants to provide me the answer as a rational number. Can something be done to change this answer to something more "convenient"?

 

[GregLocock]

Are you doing something in the symbolic toolbox?

Get hold of the numerator, float it, ditto denominator, divide one by the other. use whos to check your data types, i expect they are currently int32.

Cheers

Greg Locock


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[IRstuff]

Matlab allows you to change the number type with commands like single() and cast()

TTFN (ta ta for now)
I can do absolutely anything. I'm an expert!

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[GregLocock]

As usual a bit of context would save our time, if not the OPs. I realise that in every case Matlab scripts and screenshots are top secret, but...

Cheers

Greg Locock


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[midsidenode]

Thanks to both of you for taking the time to respond. The enclosed file is from whos. You can see that there are symbols and double variables. As I said in the previous post, the script kicks out the correct answer every time I use it with different variables, but it is displayed like this:

I1 =
765579986917712557162455387676757216362297431867076221475784577824413513977414677006199684411213333331405708899715649333325089375*w00^2)/5949503719112237390567237772294939358455642146678530973561839157469652121126802112426702893957437563628320908225210224738304
+
388505692027172886012134637830510594533891171686402955435619038358513667741636109828196480582119123127999956781721252082528717154149307180539400149802561324081218178783535*w00*w02)/120766797594289323271729746591624604509341479053326093708038601607859973196548763266756055205685080561326988000984443036792658708157593364241965896045846273396780650463232
+
590987384944035213478982883660499250847905383779439912647190361066239052187049718131701916610166590093456901248443311183944474602988196042066240822390115953505787241395277879521350174108776267888925061*w00*w11)/2508228255056559327717299405517639477515382672702395372151508761915556027554073725754578846110147691358081325939263447624692646145908262187541873345685902047135936580242368983360130194608842238078734041088
+
174827569426090409885298372444891464654962343042130332930150353940817659379606939392857334097927698681480532980427819676976840747612780277066023604711310753137386275236880975*w00*w20)/34780837707155325102258167018387886098690345967357914987915117263063672280606043820825743899237303201662172544283519594596285707949386888901686178061203726738272827333410816

which is obviously ridiculous. How can I get it to display something like this:

I1 = 128679.64*w00^2 + 3.21*w00*w02 + .000231*w00*w11 + 5.03*w00*w20

 

[GregLocock]

https://au.mathworks.com/help/symbolic/vpa.html

Cheers

Greg Locock


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[midsidenode]

Thank you Greg. Thanks a lot.
'problem solved

 

[midsidenode]

Here's another question. Maybe you guys could possibly help me. Solving a system of linear equations in Matlab is obviously a basic maneuver. I other words, if I had equation#1 as 2x+4y=3 and equation#2 as 6x+4y=5, I would obviously go to the command window and type something like A=[2 4;6 4] and B=[3;5]. Then I could obviously get the answers for x and y by inv(A)*B.
But my question is this: Deep within my Matlab script, a system of linear equations that has 9 equations and 9 unknowns is eventually produced. Once the unknowns are calculated, they are subsequently used as my script continues on with further calculations. I don’t want to have to go to the command window and manually create matrices in order to obtain the unknowns like in the example I gave. Is there a technique that can be used to separate the equation coefficients from the equation symbols and create a matrix from them?

 

[midsidenode]

I’ll try to be more clear with my last question.
What if I had a symbolic equation defined as:
V=1a+2b+3c+4d+5e+6f+7g+8h+9i
And I had eight additional equations of similar form.
Is there a command or technique that I could use to extract the coefficients and create a 9x9 matrix without going to the command window?