Constraining the size of an argument

The function is now almost complete, and ready for building and testing.

It needs one more piece of work: we need to constrain the size of the matrix Z to be the same width as X and the same height as Y. Our core function, LinearInterp2D() assumes that these constraints have been satisfied.

Launch the Argument Editor for Z. There are several ways to do this:

1. In the XLL+ ToolWindow, select INTERP2D in the upper half of the window, and double-click on Z in the lower half.
2. Launch the XLL+ Function Wizard to edit INTERP2D, and select Z. Then click on the Details tool just above the argument grid.
3. Alternatively, in the XLL+ Function Wizard, select Z and press ALT+Enter.

In the Argument Editor, select the Matrix tab:

In the Constraints group box, use the "Height is equal to" and "Width is equal to" combo-boxes to set the constraints:

Bounding variables

The result of these changes will be to create two new bounding variables, sizeOfX and sizeOfY. These will be set to the sizes of X and Y respectively when X and Y are evaluated. They they will then be checked against the height and width of Z respectively.

// Named bounds 
long sizeOfX = -1;
long sizeOfY = -1;
// Validate and translate inputs
XlReadVector(*X_op, X, L"X", XLA_TRUNC_ONEMPTY|XLA_TRUNC_ONBLANK, &sizeOfX);
XlReadVector(*Y_op, Y, L"Y", XLA_TRUNC_ONEMPTY|XLA_TRUNC_ONBLANK, &sizeOfY);
XlReadMatrix(*Z_op, mtx_adapter(Z), L"Z", XLA_TRUNC_ONEMPTY|
    XLA_TRUNC_ONBLANK, &sizeOfY, 0, &sizeOfX);

If either constraint fails, then an exception will be thrown, and an appropriate message will be returned to Excel, e.g.: Expected 5 rows for Z.

Displaying the constraints

You can see the constraints displayed in the Function Wizard:

They will also show up in the Properties window when you select X, Y or Z in the ToolWindow:

Validation errors

Build and run the add-in.

Try out the validation code. If you are using English as your language, you can get errors such as the following:

#ERROR: Expected 3 columns in Z
#ERROR: Expected 3 rows in Z
#ERROR: Expected number for Z[1,4]

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