How to reduce dimension of griddedinterpolant?

I have a gridded efficiency map where each point depends on different input values for current and voltage.

F = griddedInterpolant(x_voltage,y_current,eff_map)
% and query points 
eff = F(voltage_set,current_set)

Now I want to convert this map while runtime of a program to a curve for a fixed voltage, so that the efficiency just depends on the current/power.

Kind of,

function new_F = reduceDimension(F,fixed_voltage)
    ...
end

eff = new_F(power_set)

I can't find a quick solution, maby someone has an idea.

THX

Answer 1

[John D'Errico]

whos
  Name             Size               Bytes  Class     Attributes
  eff_map        500x500            2000000  double              
  x_voltage      500x500            2000000  double              
  y_current      500x500            2000000  double       

We are given some data as arrays, and you understand how to use griddedInterpolant. What you need to learn next is about building a function handle.

F = griddedInterpolant(x_voltage,y_current,eff_map)

Now, you want to reduce that, for a FIXED voltage, to a function of only one variable. Since 42 is the answer to everything, I'll fix the voltage at 42.

FixedVolts = 42;
F_v42 = @(y) F(repmat(FixedVolts,size(y)),y);

That is all it takes. We can now evaluate the new function at some value or a list of values for the current. We can even plot it as a function of one variable now. I've even set up F_42v in such a way that we can even pass in a complete vector or array for y. The result will be the same shape and size as the input for y.

F_v42(17)
ans =
         0.881963765526607
         
F_v42([1 3 5])
ans =
        0.0952082740655224         0.230322190630928         0.381508409480828
         
fplot(F_v42,[0,50])
xlabel 'y_current'
ylabel 'eff_map @ x = 42'

[Konrad Warner]

Perfect, thanks!

Just, to get rid of the original map data I create a new griddedInterpolant with reduced dimentions by using output arguments of fplot, or speaks something against it?

[x,y] = fplot(F_v42,[0,50])
F_v42 = griddedInterpolant(x,y)

The result looks fine, but I get a lot of warnings using fplot. No idea what that means.

Warning: Function behaves unexpectedly on array inputs. To improve performance, properly vectorize your
function to return an output with the same size and shape as the input arguments. 
> In matlab.graphics.function.FunctionLine>getFunction
  In matlab.graphics.function/FunctionLine/updateFunction
  In matlab.graphics.function.FunctionLine.set.Function_I
  In matlab.graphics.function.FunctionLine.set.Function
  In matlab.graphics.function.FunctionLine
  In fplot>singleFplot (line 245)
  In fplot>@(f)singleFplot(cax,{f},limits,extraOpts,args) (line 200)
  In fplot>vectorizeFplot (line 200)
  In fplot (line 166) 
Warning: Having two output arguments for fplot will be removed in a future release. Use the XData and YData
properties instead. 
> In fplot (line 180)