RC2_PARAM_RANGE_INVERTED

Param <name> declares min above max (or opt_min above opt_max). A range that runs backwards is empty.

What it means

min is the smallest value the parameter may hold and max is the largest. Written the other way round they describe a range with nothing in it: there is no value the parameter may take, no stop for a slider to offer, and no dimension for the optimizer to walk.

It used to compile green. The attribute took the two numbers as written, the optimizer’s from > to grid produced no dimension at all, and the control drew a slider whose thumb could not move — a parameter that looked tunable and was not.

Why it happens

Two numbers typed in the order they came to mind:

class BackwardsRange(Strategy):
    period = Param(20, min=200, max=2)
    trade = Symbol()
    sizing = FixedCapital()

    def execute(self):
        sma = SMA(self.period, on=self.trade)
        if sma.value > 0 and self.trade.is_flat:
            self.buy(self.trade)

The optimizer pair has the same rule:

class BackwardsOptRange(Strategy):
    period = Param(20, min=2, max=200, opt_min=100, opt_max=10)
    trade = Symbol()
    sizing = FixedCapital()

    def execute(self):
        sma = SMA(self.period, on=self.trade)
        if sma.value > 0 and self.trade.is_flat:
            self.buy(self.trade)

How to fix it

Swap them. A range where the two ends are EQUAL is legal — it is a constant, which is a thing an author sometimes means.

class FixedRange(Strategy):
    period = Param(20, min=2, max=200, opt_min=10, opt_max=100)
    trade = Symbol()
    sizing = FixedCapital()

    def execute(self):
        sma = SMA(self.period, on=self.trade)
        if sma.value > 0 and self.trade.is_flat:
            self.buy(self.trade)

Related

• Param()
• RC2_PARAM_DEFAULT_OUT_OF_RANGE — the ends are the right way round, but the default is not between them.
• RC2_PARAM_INT_BOUND — the ends are fractional on an integer parameter.