How do you declare a symbolic function of time as a real variable

Hello,

I have several symbolic functions of time which I would like to declare as real. How can I do this?

syms x1(t) x2(t) x3(t) real

does not work because later when I say X = [x1 ; x2 ; x3], the expressions for X involve conjugates.

Thank you,

Kevin

[Ezequiel Garcia]

bump

Answer 1

[Walter Roberson]

You could try adding an assumption that imag(x1(t)) == 0

[Walter Roberson]

You can

assumeAlso(diff(x1(t),t),'real')
assumeAlso(diff(x2(t),t),'real')

Answer 2

[Azzi Abdelmalek]

syms t
x1=sin(t) % Example

[Kevin Bachovchin]

It's an unknown (but real) function of t.

[Azzi Abdelmalek]

If x1 is unknown, how will you define it?

[Kevin Bachovchin]

I define it as syms x1(t). Is there some I can define it so that when I enter:

x1'

it says x1 and not conj(x1(t))?

[Azzi Abdelmalek]

Use x1.'  instead of x1'

syms x1 x2
x=[x1;x2]
x.'

[Kevin Bachovchin]

If I declare them like that, then they aren't functions of t, so when I differentiate with respect to t, I get 0.

[Azzi Abdelmalek]

they become function of t when you define them

[Kevin Bachovchin]

The following code

syms x1(t) x2(t)

X = [x1(t) x2(t)]

diff(X,t)

yields [ diff(x1(t), t), diff(x2(t), t)]

The following code

syms x1(t) x2(t)

X = [x1(t) ; x2(t)]

diff(X,t)

yields

[ diff(conj(x1(t)), t)

 diff(conj(x2(t)), t)]

Is there any way I can declare x1 and x2 so that I get

[ diff(x1(t), t)

 diff(x2(t), t)]