function logspace( a, b, len ) {
	if ( !isNumber( a ) || isnan( a ) ) {
		throw new TypeError( format( 'invalid argument. Exponent of start value must be numeric. Value: `%s`.', a ) );
	}
	if ( !isNumber( b ) || isnan( b ) ) {
		throw new TypeError( format( 'invalid argument. Exponent of stop value must be numeric. Value: `%s`.', b ) );
	}
	if ( arguments.length < 3 ) {
		len = 10;
	} else if ( !isNonNegativeInteger( len ) ) {
		throw new TypeError( format( 'invalid argument. Length must be a nonnegative integer. Value: `%s`.', len ) );
	}
	return gen( a, b, len );
}
Generates a logarithmically spaced numeric array.

@param {number} a - exponent of start value
@param {number} b - exponent of end value
@param {NonNegativeInteger} [len=10] - length of output array
@throws {TypeError} first argument must be numeric
@throws {TypeError} second argument must be numeric
@throws {TypeError} third argument must be a nonnegative integer
@returns {Array} logarithmically spaced numeric array

@example
var arr = logspace( 0, 2, 6 );
// returns [ 1, ~2.5, ~6.31, ~15.85, ~39.81, 100 ]