CODEWITHSUNDEEP
mathsolvermaple
Jamgreen
Jamgreen

Reputation: 11039

Positive solutions with fsolve in Maple

In Maple I use

solve(abs(-5.58 * L^(-1.88)) = 3, L);

and I get the results

L = 1.39 or L = -1.39

but if I use

fsolve(abs(-5.58 * L^(-1.88)) = 3, L);

I only get the result

L = -1.39

How can I make sure I get the positive result using fsolve?

Upvotes: 1

Views: 2693

Answers (3)

AmirHosein Sadeghimanesh
AmirHosein Sadeghimanesh

Reputation: 478

You can tell Maple to assume your variable in your expression is positive or any other kind of similar assumption. Here is one way to do it.

eq:=abs(-5.58*L^(-1.88)) assuming L>0;

Then ask Maple to solve it by fsolve, it will automatically look for only positive solutions.

fsolve(eq = 3, L)

I received this result from Maple (2019).

1.391098714

Upvotes: 0

Carl Love
Carl Love

Reputation: 1471

I'd avoid the avoid option. You can specify a range in which you want the solutions to fall, like this:

fsolve(abs(-5.58 * L^(-1.88)) = 3, L= 0..infinity);

Upvotes: 1

Lutz Lehmann
Lutz Lehmann

Reputation: 25972

https://www.maplesoft.com/support/help/maple/view.aspx?path=fsolve : "For a general equation or system of equations, the fsolve command computes a single real root. "

https://www.maplesoft.com/support/help/maple/view.aspx?path=fsolve%2fdetails : "Using the avoid option to find additional solutions"

S1:=fsolve(abs(-5.58 * L^(-1.88)) = 3, L );
S2:=fsolve(abs(-5.58 * L^(-1.88)) = 3, L, avoid = { S1 });

etc.

Upvotes: 0

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