test exponential scale with reverse range

config/grid.yaml

@@ -46,10 +46,15 @@ exchangeStrategies:
 - on: max
   grid:
     symbol: BTCUSDT
-    quantity: 0.001
+    # quantity: 0.001
+    scaleQuantity:
+      byPrice:
+        exp:
+          domain: [20_000, 30_000]
+          range: [0.2, 0.001]
     gridNumber: 30
     profitSpread: 50.0
-    upperPrice: 26800.0
+    upperPrice: 20_000.0
-    lowerPrice: 26500.0
+    lowerPrice: 30_000.0
     long: true
 

pkg/bbgo/scale_test.go

@@ -8,7 +8,7 @@ import (
 	"github.com/c9s/bbgo/pkg/fixedpoint"
 )
 
-func TestExpScale(t *testing.T) {
+func TestExponentialScale(t *testing.T) {
 	// graph see: https://www.desmos.com/calculator/ip0ijbcbbf
 	scale := ExponentialScale{
 		Domain: [2]float64{1000, 2000},
@@ -28,6 +28,25 @@ func TestExpScale(t *testing.T) {
 	}
 }
 
+func TestExponentialScale_Reverse(t *testing.T) {
+	scale := ExponentialScale{
+		Domain: [2]float64{1000, 2000},
+		Range:  [2]float64{0.1, 0.001},
+	}
+
+	err := scale.Solve()
+	assert.NoError(t, err)
+
+	assert.Equal(t, "f(x) = 0.100000 * 0.995405 ^ (x - 1000.000000)", scale.String())
+	assert.Equal(t, fixedpoint.NewFromFloat(0.1), fixedpoint.NewFromFloat(scale.Call(1000.0)))
+	assert.Equal(t, fixedpoint.NewFromFloat(0.001), fixedpoint.NewFromFloat(scale.Call(2000.0)))
+
+	for x := 1000; x <= 2000; x += 100 {
+		y := scale.Call(float64(x))
+		t.Logf("%s = %f", scale.FormulaOf(float64(x)), y)
+	}
+}
+
 func TestLogScale(t *testing.T) {
 	// see https://www.desmos.com/calculator/q1ufxx5gry
 	scale := LogarithmicScale{
@@ -63,7 +82,6 @@ func TestLinearScale(t *testing.T) {
 	}
 }
 
-
 func TestQuadraticScale(t *testing.T) {
 	// see https://www.desmos.com/calculator/vfqntrxzpr
 	scale := QuadraticScale{