Find value of a constant given a value of z(x,y)

I have the following simplified function:

constant = 5;
z = @(x,y) x + y + constant;

If I want z(4,4) to equal '0', how can I find what value the 'constant' has to be to get me that? I know that I can do a simple arithmetic in the equation above, but what if it's a more complex, multivariate function where it gets really difficult to solve for a variable like that? How can I find the value of 'constant' in that instance?

Thanks

Answer 1

[Star Strider]

Add ‘constant’ to your argument list and use the fzero function is one approach:

z = @(x,y,constant) x + y + constant;
x = 4;
y = 4;
const = fzero(@(constant) z(x,y,constant), 1)

const =
    -8

[A]

Thanks... what if I want z(x,y) to equal something other than 0?

[Matt J]

If you want z(x,y)=b, then redefine z as z_new(x,y)=z(x,y)-b

[A]

Hi Matt... can't seem to get it to work.

If I want z(4,4,constant) = 4, then how can I solve for constant?

Thanks

[Torsten]

z = @(x,y,constant) x + y + constant;
x = 4;
y = 4;
const = fzero(@(constant) z(x,y,constant)-4, 1)

[A]

This works. Thank you so much!

[Star Strider]

Our pleasure!