feat: support smoother functions with nbins setting

Co-authored-by: Chih-hsiang Cheng <ahsiang.c@gmail.com>

probfit/costfunc.pyx

@@ -641,7 +641,7 @@ cdef class Chi2Regression:
         return 1.0
 
     def draw(self, minuit=None, ax=None, parmloc=(0.05, 0.95), print_par=True,
-             args=None, errors=None, parts=False, no_plot=False):
+             args=None, errors=None, parts=False, nbins=None, no_plot=False):
         """
         Draw comparison between points (**x**,**y**) and the function **f**.
 
@@ -666,13 +666,16 @@ cdef class Chi2Regression:
 
             - **no_plot** Set this to true if you only want the return value
 
+            - **nbins** draw the PDF curve using this number of bins, 
+              instead of (if None) using the data binning.
+
         **Returns**
 
         ((data_x, data_y), (errorp,errorm), (total_pdf_x, total_pdf_y), parts)
         """
         return plotting.draw_x2(self, minuit=minuit, ax=ax, parmloc=parmloc,
                                 print_par=print_par, args=args, errors=errors, parts=parts,
-                                no_plot=no_plot)
+                                no_plot=no_plot, nbins=nbins)
 
     def show(self, *arg, **kwd):
         """

probfit/plotting.py

@@ -239,7 +239,7 @@ def draw_residual_ulh(self, minuit=None, bins=100, ax=None, bound=None,
 
 
 def draw_x2(self, minuit=None, ax=None, parmloc=(0.05, 0.95), print_par=True,
-            args=None, errors=None, grid=True, parts=False, no_plot=False):
+            args=None, errors=None, grid=True, parts=False, nbins=None, no_plot=False):
     from matplotlib import pyplot as plt
     error_ret = None
     part_ret = []
@@ -262,7 +262,11 @@ def draw_x2(self, minuit=None, ax=None, parmloc=(0.05, 0.95), print_par=True,
     draw_arg = [('lw', 2), ('zorder', 2)]
     draw_arg.append(('color', 'r'))
 
-    total_ret = draw_pdf_with_midpoints(self.f, arg, x, ax=ax, no_plot=no_plot, **dict(draw_arg))
+    # Draw PDF curve(s)
+    if nbins is not None:
+        x = np.linspace(x[0],x[-1], nbins)
+
+    total_ret = draw_pdf_with_midpoints(self.f, arg, x, no_plot=no_plot, ax=ax, **dict(draw_arg))
 
     if not no_plot:
         ax.grid(grid)