updating branch and adding another test (#640)

* Fix for #634 (#638)

squashed commits as some the earlier commit were later reversed

* Added exposure adjustment to barnzehn.py. Updated ptf example gallary with exposure adjustments to match paper.

* fixed bug when not passing sample_weight to BarnettZehnwirth.fit. updated plot_ptf_resid in gallery.

* removed sample_weight from barnettzehnwirth.fit

* unremoved sample_weight from barnettzehnwirth.fit -- the estimator ignores it as it did originall

* fixed graph title

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Co-authored-by: danielfong-act <[email protected]>

* adding another test for bz

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Co-authored-by: danielfong-act <[email protected]>
Co-authored-by: danielfong-act <[email protected]>

Author: 3 people

chainladder/development/tests/test_barnzehn.py

@@ -26,6 +26,11 @@ def test_drops():
         np.around(cl.BarnettZehnwirth(formula='C(development)',drop_valuation='1979').fit(abc).triangle_ml_.values,3)
         == np.around(cl.BarnettZehnwirth(formula='C(development)',drop = [('1977',36),('1978',24),('1979',12)]).fit(abc).triangle_ml_.values,3)
     )
+    assert np.all(
+        np.around(cl.BarnettZehnwirth(formula='C(development)',drop_valuation='1979').fit(abc).ldf_.values,3)
+        == np.around(cl.BarnettZehnwirth(formula='C(development)',drop = [('1977',36),('1978',24),('1979',12)]).fit(abc).ldf_.values,3)
+    )
+
 
 def test_bz_2008():
     '''