Wrong answer when using the SOLVE function using SYMS variables

2016 12 16

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Following is the code I am using:

syms a b c d
assume([a b c d],'real')
c1 = a + 1i*b;
c2 = c + 1i*d;
eqn = 2*c1 + 1i*3*c2;
solve(eqn==0,a)

The correct answer is 3d/2. While I do get this answer with the correct condition:

The solutions are valid under the following conditions: in(-b*1i - (c*3i)/2, 'real').

it is mathematically impossible for the given condition to be valid under the given assumption.

Is this a bug in the symbolic engine or is there something that can be done to get the correct answer?

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Thanks for the reply. Even if b = -1.5*c, shouldn't the answer still be 3*d/2? This is because a is assumed to be real...

Torsten 2016-12-16

I thought you meant that you get the answer

a = 3*d/2

from MATLAB under the condition that

-b*1i - (c*3i)/2 is 'real'

and that you think this answer is wrong.

If this is not your question, please try to formulate it more clearly.

Best wishes

Torsten.

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