"solve" Function

I'm trying to use the "solve" function to find a variable, but the other variables in the equation are input as opposed to defined. How do I fix this? Here's to illustrate what I'm trying to do using a simplified equation:

x=input('x = ')
y=input('y = ')
z=solve('x+y=z',z)

[Tebikew Alemu]

How i can write a matlab cod for a funtion

[Walter Roberson]

@Tebikew Alemu

Example:

syms x
y(x) = sin(x) - x^3/27   %this is the code for the function

y(x) = 

fplot(y, [-2*pi 2*pi])

Answer 1

[Walter Roberson]

Did you solve the license problem? Until you have the software installed and licensed, solve() isn't going to work.

The answer you are looking for is along these lines:

syms x y z
xin = input('x =');
yin = input('y =');
zsol = solve('z-y=x', z);
disp(['z = ' char(zsol)]);
znum = double(subs(zsol, {x, y}, {xin, yin}));
disp(['z = ' num2str(znum)]);

[Patrick Star]

I installed the software and this works. Thanks!

Answer 2

[Andrew Newell]

Here is one way:

x=sym(input('x = '))
y=sym(input('y = '))
syms z
z=solve(z-x-y,z)

[Patrick Star]

I tried that, but it returns this error:

??? Undefined function or method 'sym' for input arguments of type 'double'.

Error in ==> test at 1

x=sym(input('x = '))

[Walter Roberson]

Do you have the symbolic toolbox? What happens if you try

sym('x')

and

sym('1')

?

You do not really need the sym() calls for x and y:

x = input('x = ');

y = input('y = ');

syms z

z = solve(z-x-y,z);

[Patrick Star]

I don't think I have the symbolic toolbox because this is what it returns when I try sim('x'):

??? Undefined function or method 'sym' for input arguments of type 'char'.

Error in ==> test at 1

sym('x')

[Andrew Newell]

Oh. I assumed that you were actually using the command "solve", which is in the Symbolic Toolbox.

[Walter Roberson]

Please check to see whether you are licensed for the symbolic toolbox but perhaps have just not installed it. If you happen to be using the Student Edition than this could be the difficulty.

solve() is part of the symbolic toolbox and requires that toolbox be installed and licensed.

Answer 3

[Andrew Newell]

Is this what you're after?

x=input('x = ')
y=input('y = ')
z = x+y

[Patrick Star]

In a way, yes. But the equations and variables are a lot more complicated than that and I don't have it already solved. I need to solve for z and find its value, but I can't figure out how to make the solve function give me both; in other words, I have an equation like z-y=x, and I want to input 1 and 2 for x and y and then have the output give me two things:

z = x+y

and

z = 3