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I want to solve this Eqn for qpl(s):

L(s) = qpl(0) - Kel*qpl(s) - s*qpl(s) + (Nh0*Rh*fplh)/s - (Nc0*Rc*fplc)/(Kgr - s)

When I tried to solve it using "solve" function, an error appeared and I do not understand what is the mistake. I know that if I want to solve such equation I should type:

S = solve(eqn, var)

So I wrote:

syms Kel Nh0 Rh fplh Nc0 Rc fplc Kgr real

syms qpl(s) s

L(s) = qpl(0) - Kel*qpl(s) - s*qpl(s) + (Nh0*Rh*fplh)/s - (Nc0*Rc*fplc)/(Kgr - s);

S = solve (L(s),qpl(s))

But error appeared. Any help?

Walter Roberson
on 17 May 2016

Yes, changing from function to variable is the way to proceed. MrCov, you should repost as an Answer

David Coventry
on 17 May 2016

Was the error that it couldn't find an explicit solution? If so, thats because when it tried so solve, it simply couldn't find any way to solve for qpl(s).

Speaking of which, I'm not sure what you are trying to do with your notation, but if you are writing L(s) meaning that L is a function of s, try writing those variables as X_s instead, which declares them as variables in the workspace which Matlab can interpret and solve for.

syms Kel Nh0 Rh fplh Nc0 Rc fplc Kgr real

syms qpl_s s

L_s = qpl(0) - Kel*qpl_s - s*qpl_s + (Nh0*Rh*fplh)/s - (Nc0*Rc*fplc)/(Kgr - s);

S = solve (L_s,qpl_s);

this gets me a solution of qpl_s as

S =

(qpl(0) + (Nh0*Rh*fplh)/s - (Nc0*Rc*fplc)/(Kgr - s))/(Kel + s)

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