If your known points are properly gridded, you first need to convert them into a grid:
Speed = [22 22 22.5 22.5];
Angle = [130 180 130 180];
RPM = [91.1490 91.2120 93.2234 93.2860];
Speedgrid = reshape(Speed, [2 2]);
Anglegrid = reshape(Angle, [2 2]);
RPMgrid = reshape(RPM, [2 2]);
g = griddedInterpolant(Anglegrid, Speedgrid, RPMgrid); %Angle and speed need to be in this order, or the whole lot transposed
%query for speed = 25, angle = 150:
rpm25_150 = g([150, 25])
Using scattered interpolant:
s = scatteredInterpolant(Speed', Angle', RPM')
rpm25_150 = s([25, 150])
