MATLAB Answers


Need to solve this

Asked by Abdullah Azzam on 1 Jun 2019
Latest activity Commented on by Walter Roberson
on 12 Jul 2019 at 7:47
Hi guys I need away to solve these 3 equations and get the value of a b and c
a+b = 204
a+b*exp(-105*c) = 192.6
a+b*exp(-180*c) = 177.6
I have tried to use vpasolve but it gives wrong answer. What other way to use?


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2 Answers

Answer by Stephan
on 1 Jun 2019

I assume you want real Solutions. Then try:
syms a b c
assume ([a b c], 'real')
eq = [a+b == 204;...
a+b*exp(-105*c) == 192.6;...
a+b*exp(-180*c) == 177.6];
[a, b, c] = vpasolve(eq,[a b c])
Best regards


It gives wrong output it just make a=204 and b=0 and solve for c but when you substitute the result back in ghe equations you can varify they are wrong answers
Walter Roberson
on 12 Jul 2019 at 7:47
vpasolve() works to finite precision according to the digits() setting, and the calculations are suffering from massive loss of precision.
You can give a search range:
[A,B,C] = vpasolve(eq,[a b c],[200 230;-50 -1/2;-5 5])

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Answer by Alex Sha on 12 Jul 2019 at 6:52

Hi, How about the results belows:
a: 214.703486863113
b: -10.7034868631133
c: -0.00690634104047918


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