Help with imaginary number output from CAS
06-15-2014, 11:35 PM (This post was last modified: 06-15-2014 11:41 PM by Rich.)
Post: #1
 Rich Junior Member Posts: 47 Joined: Jan 2014
Help with imaginary number output from CAS
Hi, when "complex" option in the CAS settings is checked, I am getting a "_x" in the output. Is this the correct result and should interpret this as something significant?

I think this was seen in an another error earlier but I am unsure if this is what should be expect when having this setting checked.

I have attached a screenshot that has both results, the first with the "complex" checked and the second with it off.

Thanks if anyone knows the answer.
06-16-2014, 03:00 AM (This post was last modified: 06-16-2014 03:04 AM by Helge Gabert.)
Post: #2
 Helge Gabert Senior Member Posts: 460 Joined: Dec 2013
RE: Help with imaginary number output from CAS
I have noticed that same "_x" returned with a couple of expressions to be solved as well.

While I don't know why it shows up (maybe someone from the HP team knows more), what helped me in those cases was to specify an interval for the solver (e.g., x=-2 .. 2 instead of just x), which returns the solution [-1 1] without any problems (with "complex" checked).

[edit: in your case that would be w = -2 . . 2].
06-16-2014, 09:31 AM
Post: #3
 Nigel (UK) Senior Member Posts: 347 Joined: Dec 2013
RE: Help with imaginary number output from CAS
(06-15-2014 11:35 PM)Rich Wrote:  Hi, when "complex" option in the CAS settings is checked, I am getting a "_x" in the output. Is this the correct result and should interpret this as something significant?

I think this was seen in an another error earlier but I am unsure if this is what should be expect when having this setting checked.

I have attached a screenshot that has both results, the first with the "complex" checked and the second with it off.

Thanks if anyone knows the answer.

My guess: _x is a free real variable. In other words, for any real value of _x there are two roots for w, given by those two complex expressions.

Nigel (UK)
06-17-2014, 06:32 AM
Post: #4
 Rich Junior Member Posts: 47 Joined: Jan 2014
RE: Help with imaginary number output from CAS
Thank you, I was able to complete my function with the suggestion of a very wide interval, though I later returned and just made an assumption that w was in the domain of a real integer.

For any future reference, this was the command assume(w, DOM_INT).
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