modify if statement for R 4.2.0

[inoue0426]

Related to #18

From the R 4.0.0,

CHANGES IN R 4.0.0
SIGNIFICANT USER-VISIBLE CHANGES:
• matrix objects now also inherit from class "array", so e.g., class(diag(1))
is c("matrix","array"). This invalidates code incorrectly assuming that
class(matrix_obj)) has length one.
S3 methods for class "array" are now dispatched for matrix objects.

The class function will return not only 'matrix' but 'array' So if comparing as 1d like if (class(A_norm) != 'matrix') does not work. Here, I tried to implement if the class(A_norm) contains a matrix, return true.

Checklist

• [x] Work correctly

[linqiaozhi]

This is great. Thank you @inoue0426!