Method sigma

MathParser/src/com/aghajari/math/Functions.java:163–165

(MathParser parser, String variableName, String exp, double from, double to)

    }

    public static double sigma(MathParser parser, String variableName, String exp, double from, double to) throws MathParserException {
        return sigma(parser, variableName, exp, from, to, 1.0);
    }

    public static double sigma(MathParser parser, String variableName, String exp, double from, double to, double step) throws MathParserException {
        if (!Utils.isIdentifier(variableName))