How to use generated code from cftool to find unknown variables

I have three variables x y and z where x is speed (mx1 array), y is torque (nx1 array), z is efficiency (mxn array). This is a motor data. On using auto fit in cftool it chose interpolant-linear.

I want to find efficiency (z)of the motor at any given speed and torque (i.e x and y). I don't know what to do after generating the code and saving the results in workspace.

[Walter Roberson]

"interpolant-linear" is the same as interp2(); you do not need cftool for that.

[DARSHAN N KANNUR]

okay, let me know how to find z value when x and y are given. x y z all three set of values are defined and also let me know to use interp2 to procced.

[Walter Roberson]

z_at_query = interp2(x, y, z.', x_query, y_query)

The .' on z is important. Your data has x going down columns, but in MATLAB x goes across rows.

[DARSHAN N KANNUR]

Thank you so much. it worked. How to accept your answer.

Answer 1

[Steven Lord]

The fitted object you export to the workspace is an sfit object. You can evaluate an sfit object by passing the values at which you want to evaluate it into the object as shown in the example on that documentation page. The same holds for cfit objects:

load census
f = fit(cdate, pop, 'poly2')

f = 
     Linear model Poly2:
     f(x) = p1*x^2 + p2*x + p3
     Coefficients (with 95% confidence bounds):
       p1 =    0.006541  (0.006124, 0.006958)
       p2 =      -23.51  (-25.09, -21.93)
       p3 =   2.113e+04  (1.964e+04, 2.262e+04)

plot(cdate, pop, 'o-') % show the data
hold on
plot(1985, f(1985), 'x') % show the fitted value for 1985

The X looks to be pretty close to the line.

[DARSHAN N KANNUR]

could you please edit the code and send as per my requirement. where x, y, z variables are plotted using cftool with interpolant linear. where i should find z value for any x and y input.

Answer 2

[Walter Roberson]

The use of interpolant in this case can be replaced by just calling interp2() without using cftool at all.

x y and z where x is speed (mx1 array), y is torque (nx1 array), z is efficiency (mxn array).

z_at_query = interp2(x, y, z.', x_query, y_query)

The .' on z is important. Your data has x going down columns, but in MATLAB x goes across rows.