Inverse Fast Walsh–Hadamard transform
y = ifwht(x)
y = ifwht(x,n)
y = ifwht(x,n,ordering)
y = ifwht(x) returns the coefficients of the inverse discrete fast Walsh-Hadamard transform of the input x. If x is a matrix, the inverse fast Walsh-Hadamard transform is calculated on each column of x. The inverse fast Walsh-Hadamard transform operates only on signals with length equal to a power of 2. If the length of x is less than a power of 2, its length is padded with zeros to the next greater power of two before processing.
y = ifwht(x,n) returns the n-point inverse discrete Walsh-Hadamard transform, where n must be a power of 2.
y = ifwht(x,n,ordering) specifies the ordering to use for the returned inverse Walsh-Hadamard transform coefficients. To specify the ordering, you must enter a value for the length n or, to use the default behavior, specify an empty vector () for n. Valid values for the ordering are the following strings:
|'sequency'||Coefficients in order of ascending sequency value, where each row has an additional zero crossing. This is the default ordering.|
|'hadamard'||Coefficients in normal Hadamard order.|
|'dyadic'||Coefficients in Gray code order, where a single bit change occurs from one coefficient to the next.|
 Beauchamp, Kenneth G. Applications of Walsh and Related Functions: With an Introduction to Sequency Theory. London: Academic Press, 1984.
 Beer, Tom. "Walsh Transforms." American Journal of Physics. Vol. 49, 1981, pp. 466–472.