Dies ist mein zweiter Versuch, Gradientenabstieg in einer Variablen zu implementieren, und es divergiert immer. Irgendwelche Ideen?Warum divergiert der einfache Gradientenabfall?
Dies ist eine einfache lineare Regression zur Minimierung der Restsumme von Quadraten in einer Variablen.
def gradient_descent_wtf(xvalues, yvalues):
tolerance = 0.1
#y=mx+b
#some line to predict y values from x values
m=1.
b=1.
#a predicted y-value has value mx + b
for i in range(0,10):
#calculate y-value predictions for all x-values
predicted_yvalues = list()
for x in xvalues:
predicted_yvalues.append(m*x + b)
# predicted_yvalues holds the predicted y-values
#now calculate the residuals = y-value - predicted y-value for each point
residuals = list()
number_of_points = len(yvalues)
for n in range(0,number_of_points):
residuals.append(yvalues[n] - predicted_yvalues[n])
## calculate the residual sum of squares from the residuals, that is,
## square each residual and add them all up. we will try to minimize
## the residual sum of squares later.
residual_sum_of_squares = 0.
for r in residuals:
residual_sum_of_squares += r**2
print("RSS = %s" % residual_sum_of_squares)
##
##
##
#now make a version of the residuals which is multiplied by the x-values
residuals_times_xvalues = list()
for n in range(0,number_of_points):
residuals_times_xvalues.append(residuals[n] * xvalues[n])
#now create the sums for the residuals and for the residuals times the x-values
residuals_sum = sum(residuals)
residuals_times_xvalues_sum = sum(residuals_times_xvalues)
# now multiply the sums by a positive scalar and add each to m and b.
residuals_sum *= 0.1
residuals_times_xvalues_sum *= 0.1
b += residuals_sum
m += residuals_times_xvalues_sum
#and repeat until convergence.
#convergence occurs when ||sum vector|| < some tolerance.
# ||sum vector|| = sqrt(residuals_sum**2 + residuals_times_xvalues_sum**2)
#check for convergence
magnitude_of_sum_vector = (residuals_sum**2 + residuals_times_xvalues_sum**2)**0.5
if magnitude_of_sum_vector < tolerance:
break
return (b, m)
Ergebnis:
gradient_descent_wtf([1,2,3,4,5,6,7,8,9,10],[6,23,8,56,3,24,234,76,59,567])
RSS = 370433.0
RSS = 300170125.7
RSS = 4.86943013045e+11
RSS = 7.90447409339e+14
RSS = 1.28312217794e+18
RSS = 2.08287421094e+21
RSS = 3.38110045417e+24
RSS = 5.48849288217e+27
RSS = 8.90939341376e+30
RSS = 1.44624932026e+34
Out[108]:
(-3.475524066284303e+16, -2.4195981188763203e+17)