public void testFFTInverse()
{
List <Complex> x = new InitializedList <Complex>(3);
x[0] = 1;
x[1] = 2;
x[2] = 3;
int order = FastFourierTransform.min_order(x.Count) + 1;
FastFourierTransform fft = new FastFourierTransform(order);
int nFrq = fft.output_size();
List <Complex> ft = new InitializedList <Complex>(nFrq);
List <Complex> tmp = new InitializedList <Complex>(nFrq);
Complex z = new Complex();
fft.inverse_transform(x, 0, 3, ft);
for (int i = 0; i < nFrq; ++i)
{
tmp[i] = Math.Pow(ft[i].Magnitude, 2.0);
ft[i] = z;
}
fft.inverse_transform(tmp, 0, tmp.Count, ft);
// 0
double calculated = ft[0].Real / nFrq;
double expected = (x[0] * x[0] + x[1] * x[1] + x[2] * x[2]).Real;
if (Math.Abs(calculated - expected) > 1.0e-10)
{
QAssert.Fail("Convolution(0)\n"
+ " calculated: " + calculated + "\n"
+ " expected: " + expected);
}
// 1
calculated = ft[1].Real / nFrq;
expected = (x[0] * x[1] + x[1] * x[2]).Real;
if (Math.Abs(calculated - expected) > 1.0e-10)
{
QAssert.Fail("Convolution(1)\n"
+ " calculated: " + calculated + "\n"
+ " expected: " + expected);
}
// 2
calculated = ft[2].Real / nFrq;
expected = (x[0] * x[2]).Real;
if (Math.Abs(calculated - expected) > 1.0e-10)
{
QAssert.Fail("Convolution(1)\n"
+ " calculated: " + calculated + "\n"
+ " expected: " + expected);
}
}
