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Real and Complex

Posted on 2008-09-13 10:25 By Zro85 (Maple Rating 1 14)
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How can i avoid this error?

that happens 'cause I have 3 different solution for Vv:

> Vv3:=Re(solve(eq1,Vv)[3]);

 

In this way I can avoid it but solutions is not real...is complex!Ideas?

 

> Vv1:=Re(solve(eq1,Vv)[1]);

> Vv2:=Re(solve(eq1,Vv)[2]);

 

> solutions:=Re(solve({eq1},{Vv}));

Error, invalid input: Re expects 1 argument, but received 3

‹ How do I make full simplification of expressions? Confused on how to work out this problem Find the value of k... ›

How can i avoid this error?

Comment on 2008-09-13 10:28 from Zro85 (Maple Rating 1 14)

How can i avoid this error?

> solutions:=Re(solve({eq1},{Vv}));

Error, invalid input: Re expects 1 argument, but received 3

that happens 'cause I have 3 different solution for Vv:

> Vv3:=Re(solve(eq1,Vv)[3]);

> Vv1:=Re(solve(eq1,Vv)[1]);

> Vv2:=Re(solve(eq1,Vv)[2]);

 

In this way I can avoid it but solutions is not real...is complex!Ideas?

 Ps:sorry for double post but i have a lot of problems to do the first one!

Axel Vogt's picture

use the command 'map'

Comment on 2008-09-13 11:01 from Axel Vogt (Maple Rating 4 955) 
  x^3+x^2+1;         # the equation
  S:=[solve(%,x)]:   # the solutions
  nops(S);           # there are 3 solutions

  map(Re,S):         # does what you want 
  simplify(%, size); # simplify it

Ty...

Comment on 2008-09-13 12:13 from Zro85 (Maple Rating 1 14)

Ty...

acer's picture

real solutions

Comment on 2008-09-13 11:51 from acer (Maple Rating 4 1377)

I suspect (but am not 100% sure) that the submitter wants to select the purely real solutions from solve's output, and not just to extract the real part of the returned solutions. Apologies, if I've interpreted that incorrectly.

Zro85, the Re() command will extract the real component. But the real component of any of the complex solutions may not also be a solution. It's not clear that you realize this, about Maple's Re() command. Is it clear?

If you search this site for the pair "RealDomain" and "solve" you will find other posts that discuss the question of getting only purely real solutions to an equation or system of equations.

acer

I understood what you

Comment on 2008-09-13 12:14 from Zro85 (Maple Rating 1 14)

I understood what you mean...I will see those articles!

Axel Vogt's picture

point taken

Comment on 2008-09-13 16:46 from Axel Vogt (Maple Rating 4 955)

Ok. But looking at x^2 + const (or similar) shows that this is a bit senseless as question, as it is too general - or needs care for the special case(s).

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