How can I plot a surface with changing constant?

Hi guys,

I have a complex question. I want to graph the following equation as a surface. However, the constant A changes with a certain value of the y-axis:

Want to graph: z = M - 10x - 3.5y

Where

M = 5 + 3 for y < 10
M = 5 + 4 for 10 < y < 20
M = 5 + 5 for 20 < y < 30

Does this make sense? The value of the constant depends on the value of the y.

How can I approach this?

Thanks

Answer 1

[Star Strider]

I suggest this as a possibility:

M = [3 4 5];
z = @(x,y)  5 + M(max(1,fix((y-30+0.1)/10)+3)) - 10.*x - 3.5.*y;

I tested the M-matrix addressing with this statement:

Mr = [y'  max(1,(fix((y-30)/10)+3))'  M(max(1,fix((y-30+0.1)/10)+3))']

The surface plot is an inclined plane.

[Walter Roberson]

There needs to be a jump at y = 10 and at y = 20

[Star Strider]

There are in the code I tested, both with the Mr test variable and with z(y) with a fixed x=15. I was expecting visible discontinuities in the surface plot with X and Y defined with meshgrid with x and y defined as [0:0.1:30], but when I looked for them in the 2D plot, they were there but barely visible.

Answer 2

[Walter Roberson]

[X, Y] = ndgrid(....);
Z = 5 - 10 * X - 3.5 * Y;

Z(10 < Y & Y < 20) = Z(10 < Y & Y < 20) + 4;

and so on.

Note: your M is not defined for Y = 10 exactly or Y = 20 exactly

[A]

Thank you for the solutions to you both.

I'm uncertain which solution is the best one to use in my case?

I want to be able to graph this as a surface?

Thank you