evalAt() does not work any way I use it

When I try using evalAt() function I always get an error. I have tried using it in many different ways.

Example 1:

y=x^2;
evalAt(y, x=3)

Error: File: plot_test.m Line: 2 Column: 12
The expression to the left of the equals sign is not a valid target for an assignment.

I also tried to use subs() and still get error.

I also tried reinstalling MATLAB and did not work.

I will really appretiate any help, Thanks

[Walter Roberson]

Which MATLAB version are you using? That syntax has only been valid since R2012a.

[Matt Fig]

But SUBS has been around for longer...

[Walter Roberson]

Yes, but the ability to use "=" in a symbolic expression (as opposed to assignment) is new in R2012a.

subs(y, x, 3)

not

subs(y, x=3)

Answer 1

[Star Strider]

Starting with 2012a, you can Create Symbolic Functions. This is probably the easiest way to do what you want:

        syms x y 

        y(x) = x^2

        z = y(3)

giving this result:

y(x) =

x^2

z =

9

Answer 2

[Matt Fig]

What do you see when you type these? Do you see the help, or do you see function not found?

help evalAt
help subs

If you see 'function not found', then you don't have the symbolic toolbox installed, or you don't have a license checked out.

Answer 3

[Sachin Ganjare]

Most probably you do not have 'Symbolic Math Toolbox' installed on your system. Check using 'ver' command.

Answer 4

[Diomedes]

Actually I have the 2012b edition and I have made sure that the Symbolic Math toolbox is install.

I found a solution to my problem. I just used the function eval() and it worked. Thanks a lot for you help.