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Simple 1D Functions

The 1D function type, IFunction1D is the simplest function type. It takes a 1D set of x values and requires the function values to be returned at those points as a numpy array. For the Mantid Fit framework to recognise the function the method that computes the values must be called function1D and takes two arguments: self and xvals.

As an example take a simple function, \(\Large y = C\sqrt{x}\). The class would look something like:

from mantid.api import *
import numpy

class Example1DFunction(IFunction1D):

    def init(self):
        self.declareParameter("C", 0.0)

    def function1D(self, xvals):
        # Access current values during the fit
        c = self.getParameterValue("C")

        return c*numpy.sqrt(xvals)

FunctionFactory.subscribe(Example1DFunction)

The current value of a named parameter is accessed using the getParameterValue method and simply returns a float value. function1D should return a numpy array of the same length as the input xvals array. This is now a working example and when loaded into Mantid it will show as an extra function named Example1DFunction in the function menus.