def calculate_target(category, lambda_vars, coefficients):
    """ Returns a target value for a given category.

        Args:
            category (str): category name.
            lambda_vars (dict of str to double): dictionary
                    that maps DMU codes to the corresponding value
                    of lambda variables.
            coefficients (dict of tuple of str, str to double}): dictionary
                that maps internal DMU code and category to the
                corresponding coefficient, e.g. {(DMU, category) : value}.

        Returns:
            double: target value.
    """
    target = 0
    for dmu, value in lambda_vars.items():
        target += value * coefficients[dmu, category]
    return target
