def constant_check(array):
    """
    Checks to see numpy array includes a constant.

    Parameters
    ----------
    array           : array
                      an array of variables to be inspected 

    Returns
    -------
    constant        : boolean
                      true signifies the presence of a constant

    Example
    -------

    >>> import numpy as np
    >>> import libpysal
    >>> from libpysal import examples
    >>> import spreg
    >>> from spreg import OLS
    >>> db = libpysal.io.open(examples.get_path("columbus.dbf"),"r")
    >>> y = np.array(db.by_col("CRIME"))
    >>> y = np.reshape(y, (49,1))
    >>> X = []
    >>> X.append(db.by_col("INC"))
    >>> X.append(db.by_col("HOVAL"))
    >>> X = np.array(X).T
    >>> reg = OLS(y,X)
    >>> spreg.constant_check(reg.x)
    True

    """
    n, k = array.shape
    constant = False
    for j in range(k):
        variable = array[:, (j)]
        varmin = variable.min()
        varmax = variable.max()
        if varmin == varmax:
            constant = True
            break
    return constant
