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Using function solve in symbolics

OpticGuy
1-Newbie

Using function solve in symbolics

Hi guys, I eventually learnt how to use the symbolics now. I have written my equation, but when I want to solve it, it requires variable. Its not integral, just algebra, I dont know why it requires variable.

Please help guys.

16 REPLIES 16

For whatever variable you want to solve this equation?

And second.

Use please * between variables!

Hi Valery, thank you for your reply. But I dont quite understand. Its just algebra solving. The only variable I have is time. From most examples I see, they variable as a number. But I want it purely to be symbolic.

If this is the equation:

If I want to solve:

real(exp(1i*w(t)+*fi(t))+(cos(wRF(t))/sin(wRF(t)))

In this case, the variable is t. But I dont even need to mention t if I want to solve algebraically, right?

I just want to solve the interaction between exp, cos, and sin. Sorry if I am describing something wrong here, but I truly dont understand.

If I have to define a variable, how do i do it in the worksheet? I knoe defining a variable in terms of number in Mathcad is going to be t:=number. Right?

Please advice! Thank you very much.

Optic Guy wrote:

If I want to solve:

real(exp(1i*w(t)+*fi(t))+(cos(wRF(t))/sin(wRF(t)))

In this case, the variable is t.

Sorry w(t) etc is a function of t?

Yes Valery, everything else is a constant...

Do you mean you want to find the square of the real part of the expression? If so, the attached might help. However, I've left out Eo since it is undefined (I assume it's a function name). You'll need to define it somewhere.

Alan

Hi Alan!! Excellent job!! Thanks a lot... Now I understand... Between, why did you use rectangular? What does it mean?

And also, for an instance, when you type assume, w=real, which "=" symbol you used, cause I realize I cant use the normal "=" symbol. And, when I redefine certain parameter, it says variable undefined, yet it solves it though.

From your worksheet, I understand that every variable needs to be defined as real in order to solve it is it? does it has to be always real?

Thanks a lot mate!

Optic Guy wrote:

... why did you use rectangular? What does it mean?

It means complex numbers are expressed in the "rectangular" form x + iy rather than in the "polar" form a.e^(i.theta).

And also, for an instance, when you type assume, w=real, which "=" symbol you used, cause I realize I cant use the normal "=" symbol.

Don't type w=real, use the symbolic menu, from where you can select "assume" and also "Modifiers" from which you can select "real" which will automatically insert an = (it's a Ctrl =).

Symbolics.PNG

And, when I redefine certain parameter, it says variable undefined, yet it solves it though.

The "variable undefined" error message affects the numerical solvers, but not the symbolic ones.

From your worksheet, I understand that every variable needs to be defined as real in order to solve it is it? does it has to be always real?

No they don't all have to be real, I just assumed they were real here. Without being told which are real and which aren't, the symbolic solver will often assume they could be complex. This can make it more difficult for it to find a simplified version of what you are after.

Alan

PS I've just noticed that in the file symb2 that I uploaded, I've used the wrong style "phi" in the argument list, and also have left "SRF" out of the argument list.

I've also noticed that, in this case, none of the "assume"s are necessary!! See attached.

Alan

Rectangular does all the job! Wow... Awesome!! Thanks a lot... I will try it out first and get back to you soon... Thanks mate!

Outstanding mate!! Thank you so much for very crisp tutorial!!

Hi Alan, thanks for your help. I need an additonal advice here. I tried looking in the guidebook. But its not explained anywhere. I try to get the absolute value of the whole equation. Its giving the same trouble as I faced earlier with the square problem.

The absolute equation is defined as B. Sorry for troubling you too much.

Looks like you have to construct it explicitly! See attached.

Alan

Hi Alan, I actually took solved it using complex conjugate... But this works as well... Thank you very much... From the your worksheet, the final answer after taking the absolte evaluation, is there any chance to further simplify it?

Thank you very much!

Optic Guy wrote:

Hi Alan, I actually took solved it using complex conjugate...

Yes, a good idea!

From the your worksheet, the final answer after taking the absolte evaluation, is there any chance to further simplify it?

Well, you could try collecting some terms together using the "collect" command, but I'm not sure you'll manage to get anything much simpler!

Alan

Hi Alan, I have used complex conjugate, it works only at times. I cant find any errors, please advice, could it be a bug?

The worksheet named: symb5 can solve the complex conjugate.

But worksheet named: symb_PD_Amnon, it doesnt solve the complex part even after complex conjugate...

Sorry for bothering you!!

Expressing the initial definitions a little more simply seems to help. See attached.

Alan

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