The reason why it is not recognized is that you must use, in this case, the MATLAB® Script Node
(right) rather that Mathscript Node
MATLAB® Script Node in LabVIEW uses ActiveX to call the MATLAB® runtime system while LabVIEW MathScript RT Module runs separately from The MathWorks, Inc. MATLAB® software.
You can find the MATLAB® Script Node
in Mathematics >> Scripts & Formulas >> Script Nodes :