Substitution problem in matlab

Hello, I'm new in matlab, and I'm trying to learn operations with variables,so I have encountered a little problem, that I don't quite understand, why

ER=subs(yp,{sx},{1})
ER=subs(yp,{sy},{1})

it's not a same thing, as

ER=subs(yp,{sx,sy},{1,1})

? In first case the answer is

-y*(exp(-x^2/sx^2)*exp(-y^2) - 1)

(and I don't want sx^2) and in the second case the answer is

-y*(exp(-x^2)*exp(-y^2) - 1)

(this is exactly, what i need)

This is my starting code:

syms x y z;
syms sx sy;
yp=y*(1-exp(-x^2/sx^2)*exp(-y^2/sy^2))

Does someone know what's the reason behind it?

[madhan ravi]

Can you format the code by selecting the whole code and clicking the code button?

Answer 1

[madhan ravi]

syms x y z; 
syms sx sy; 
yp=y*(1-exp(-x^2/sx^2)*exp(-y^2/sy^2))
ER=subs(yp,{sx},{1})
ER=subs(ER,{sy},{1}) 
ER1=subs(yp,{sx,sy},{1,1})

Reason: when you wanted to substitute for sy the second time you should type ER instead of up because you’re replacing the old equation again

TYPE:

ER=subs(ER,{sy},{1})

INSTEAD OF:

ER=subs(yp,{sy},{1})

[Michael Elman]

Thank you!

[madhan ravi]

you're welcome :)