Abstract In this work, we propose a numerical method to find an approximation of
the variable-order integral of a given function using a generalization of the modified
hat functions. First, an operational matrix of the basis functions corresponding to
the variable-order integral operator is introduced. Then, using this matrix and an
approximation of the given function, we find an approximation of the variable-order
integral operator of the function. An error estimate is proved. Two test examples are
included to show the efficiency and accuracy of our new technique. Finally, this new
technique is used to solve the variable-order differential equations numerically and
some illustrative problems are provided to validate the applicability and accuracy of
this new scheme.