What is 'mtimes' for input argument?

Hey there. I am trying to integrate the following function but there is always the error:

Undefined function 'mtimes' for input arguments of type 'cell'

How could I solve this?

cp_fill= @(T_Al2O3) A+B*(T_Al2O3./1000)+C*(T_Al2O3./1000).^2+D*(T_Al2O3./1000).^3+E/(T_Al2O3./1000).^2;  %Shomate equation
delta_H_fill_mol=integral(cp_fill,T_fill_cold,T_fill_hot); %[J/mol]
delta_H_fill=(delta_H_fill_mol/M_fill)*1000                %[J/kg]

[Stephen23]

The mtimes operator * occurs four times in your code. The mtimes operation is only defined for numeric arrays, and so obviously in one of those four locations you have (at least) one cell array instead of a numeric array, thus the error message.

Are any of A, B and/or D cell arrays?