set a variable value

def set(self, varname, value, idx=0, units=None):
        '''set a variable value'''
        if not varname in self.mapping.vars:
            raise fgFDMError('Unknown variable %s' % varname)
        if idx >= self.mapping.vars[varname].arraylength:
            raise fgFDMError('index of %s beyond end of array idx=%u arraylength=%u' % (
                varname, idx, self.mapping.vars[varname].arraylength))
        if units:
            value = self.convert(value, units, self.mapping.vars[varname].units)
        # avoid range errors when packing into 4 byte floats
        if math.isinf(value) or math.isnan(value) or math.fabs(value) > 3.4e38:
            value = 0
        self.values[self.mapping.vars[varname].index + idx] = value