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sineefit: Change sfit4 to fit to \sin instead of \cos

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And adjust the period locator accordingly.
Fitting \sin is the same mathematically, it's just conceptually more
straightforward since we're locating zero crossings anyway.
This commit is contained in:
Jim Paris 2013-04-27 18:12:20 -04:00
parent 4da658e960
commit b7c3820416
1 changed files with 8 additions and 8 deletions

16
src/sinefit.py
View File

@ -98,12 +98,12 @@ def process(data, interval, args, insert_function, final):
continue
#p.plot(arange(N), this)
#p.plot(arange(N), A * cos(f0/fs * 2 * pi * arange(N) + phi) + C, 'g')
#p.plot(arange(N), A * sin(f0/fs * 2 * pi * arange(N) + phi) + C, 'g')
# Period starts when the argument of cosine is 3*pi/2 degrees,
# Period starts when the argument of sine is 0 degrees,
# so we're looking for sample number:
# n = (3 * pi / 2 - phi) / (f0/fs * 2 * pi)
zc_n = (3 * pi / 2 - phi) / (f0 / fs * 2 * pi)
# n = (0 - phi) / (f0/fs * 2 * pi)
zc_n = (0 - phi) / (f0 / fs * 2 * pi)
period_n = fs/f0
# Add periods to make N positive
@ -149,9 +149,9 @@ def sfit4(data, fs):
Output:
Parameters [A, f0, phi, C] to fit the equation
x[n] = A * cos(f0/fs * 2 * pi * n + phi) + C
x[n] = A * sin(f0/fs * 2 * pi * n + phi) + C
where n is sample number. Or, as a function of time:
x(t) = A * cos(f0 * 2 * pi * t + phi) + C
x(t) = A * sin(f0 * 2 * pi * t + phi) + C
by Jim Paris
(Verified to match sfit4.m)
@ -191,7 +191,7 @@ def sfit4(data, fs):
s = zeros(3)
w = 2*pi*f0
# Now iterate 7 times (step i)
# Now iterate 7 times (step b, plus 6 iterations of step i)
for idx in range(7):
D = c_[cos(w*t), sin(w*t), ones(N),
-s[0] * t * sin(w*t) + s[1] * t * cos(w*t) ] # eqn B.16
@ -201,7 +201,7 @@ def sfit4(data, fs):
## Extract results
A = sqrt(s[0]*s[0] + s[1]*s[1]) # eqn B.21
f0 = w / (2*pi)
phi = -arctan2(s[1], s[0]) # eqn B.22
phi = arctan2(s[0], s[1]) # eqn B.22 (flipped for sin instead of cos)
C = s[2]
return (A, f0, phi, C)
except Exception as e: