CODEWITHSUNDEEP
matlab
user6086432
user6086432

Reputation: 53

Symbolic math equation in matlab

I am trying to enter an equation into MATLAB which contains about 5 variables. Here is what I did:

syms Pwf Pr Qo J Qmax
Pwf = Pr((1.266 - (1.25*Qo/Qmax))^2) - 0.125

I want to run it such that I can input different values for different variables per time, but it gives an error:

Invalid indexing or function definition.

How should I do it?
Thank you

Upvotes: 1

Views: 84

Answers (1)

nahomyaja
nahomyaja

Reputation: 202

From what I understand you are trying to create a function called Pwf which varies with respect to the values of Pr, Qo and Qmax

If that's the case, you can use syms command in MATLAB to create a symbolic function Pwf with independent variables Pr, Qo and Qmax

syms Pwf(Pr, Qo, Qmax)
Pwf(Pr,Qo,Qmax) = Pr*((1.266 - (1.25*Q0./Qmax))^2) - 0.125;

This creates a symbolic function Pwf and sumbolic variables Pr, Qo and Qmax. You can then assign different values for the variables and call the function Pwf

Pr = 1; 
Qo = 2;
Qmax = 10; 
Pwf(Pr, Qo, Qmax)

This would yield you a result in fractions as follows. 

ans = 113407/125000

You can get numeric output using double() or vpa() 

>> vpa(ans)
ans = 0.907256

>> double(ans)
ans = 0.9073

You have mentioned about another variable J which is not used in the equation, which can be added in to the function in a similar way. You just have to call the function Pwf(Pr, Qo, Qmax) each time you change the variable values.

Upvotes: 1

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