如何从多项式拟合中排除值？

Question

我将多项式拟合到我的数据中，如图所示：

使用脚本：

from scipy.optimize import curve_fit
import scipy.stats
from scipy import asarray as ar,exp

xdata = xvalues
ydata = yvalues

fittedParameters = numpy.polyfit(xdata, ydata + .00001005 , 3)
modelPredictions = numpy.polyval(fittedParameters, xdata) 

axes.plot(xdata, ydata,  '-')
xModel = numpy.linspace(min(xdata), max(xdata))
yModel = numpy.polyval(fittedParameters, xModel)

axes.plot(xModel, yModel)

我要排除3.4到3.55 um之间的区域。如何在脚本中做到这一点？我也试图在原始.fits文件中摆脱掉NaN。帮助将很有价值。

Answer 1

您可以屏蔽排他性区域内的值，并稍后将此屏蔽应用于您的拟合函数

# Using random data here, since you haven't provided sample data
xdata = numpy.arange(3,4,0.01)
ydata = 2* numpy.random.rand(len(xdata)) + xdata

# Create mask (boolean array) of values outside of your exclusion region
mask = (xdata < 3.4) | (xdata > 3.55)

# Do the fit on all data (for comparison)
fittedParameters = numpy.polyfit(xdata, ydata + .00001005 , 3)
modelPredictions = numpy.polyval(fittedParameters, xdata) 
xModel = numpy.linspace(min(xdata), max(xdata))
yModel = numpy.polyval(fittedParameters, xModel)

# Do the fit on the masked data (i.e. only that data, where mask == True)
fittedParameters1 = numpy.polyfit(xdata[mask], ydata[mask] + .00001005 , 3)
modelPredictions1 = numpy.polyval(fittedParameters1, xdata[mask]) 
xModel1 = numpy.linspace(min(xdata[mask]), max(xdata[mask]))
yModel1 = numpy.polyval(fittedParameters1, xModel1)

# Plot stuff
axes.plot(xdata, ydata,  '-')
axes.plot(xModel, yModel)        # orange
axes.plot(xModel1, yModel1)      # green

给予

现在绿色曲线已被拟合，但排除了3.4 < xdata 3.55。橙色曲线是没有排除的拟合（供比较）

如果您还想排除xdata中可能存在的nan，则可以通过mask函数来增强numpy.isnan()，例如

# Create mask (boolean array) of values outside of your exclusion AND which ar not nan
xdata < 3.4) | (xdata > 3.55) & ~numpy.isnan(xdata)