First of all I don't know if this method is supported, it would be very useful if not.
So if this is not a feature please forgive me because I considered as a bug.
The "InterBilinear" function gives wrong results if matrix is used for x or y value.

interpolation.sm (15 KiB) downloaded 123 time(s).

Regards

Wrote

First of all I don't know if this method is supported, it would be very useful if not.
So if this is not a feature please forgive me because I considered as a bug.
The "InterBilinear" function gives wrong results if matrix is used for x or y value.

Mathcad Bicubic can't be reproduced, even "if it could be"
would be useless whereas Smath does not have Matrix 3D plot [only 3 cols].
Your metric X,Y directions aren't correct. You can metric like center as well.
You can have surface plot, only... rotate the plot at will.

interpolation [Oterwise metric X, Y Directions].sm (33 KiB) downloaded 76 time(s).

Hi overlord. I prefer source code in a high level language, even it could be slowest.
interpolation bilinear source code.sm (26 KiB) downloaded 85 time(s).
Best regards.
Alvaro.

Wrote

You can have surface plot, only... rotate the plot at will.

You can have it otherwise from the X_Y surface plot.

interpolation [Oterwise metric X, Y Directions].sm (95 KiB) downloaded 66 time(s).

Wrote

You can have it otherwise from the X_Y surface plot.

... you can create the matrix and the X, Y directions at will.
Then just interpolate ... Spline linterp has the virtue equivalent quadratic.
It would be mistake to cspline.

Cheers ... Jean

Bilinear SplineInterp [Construct USER].sm (12 KiB) downloaded 54 time(s).

It is a bug, thank you! 4th and 5th argument type isn't checked, therefore (unintentionally) vector math applies.

Wrote

First of all I don't know if this method is supported, it would be very useful if not.
So if this is not a feature please forgive me because I considered as a bug.
The "InterBilinear" function gives wrong results if matrix is used for x or y value.

Two things here:
1. The 4th and 5th arguments are presented in reverse order compared to Mathcad
2. The two dimension spline coding is from unknown source
...neither from either Smath [linterp, cinterp, ainterp]
...could be from erroneous quadratic source code.
As given in the attached: Spline(x,y,M) assumed = Mathcad Bicubic2D(x,y,M,vx,object)
At this point, you can spline/plot/rotate the surface as suggested before

Cheers ... Jean

Bilinear SplineInterp [Construct USER].sm (24 KiB) downloaded 68 time(s).

Wrote

Two things here:

InterpBilinear(vx,vy,M,object,vector) ... does not collect"vector wise"
InterpBilinear(vx,vy,M,object,valueX) ... correct
That is the answer to the "bug",
InterpBilinear(vx,vy,M,object,vector)