Trigger fully correlated variables for corr2D very close to one (#75)

* Trigger fully correlated variables for corr2D equals one at 1e-8 accuracy

* fix white line

* Catch nearly perfect anti-correlations

Co-authored-by: chris <chris@ringeval.com>

getdist/mcsamples.py

@@ -1657,9 +1657,9 @@ def get2DDensityGridData(self, j, j2, num_plot_contours=None, get_density=False,
         has_prior = parx.has_limits or pary.has_limits
 
         corr = self.getCorrelationMatrix()[j2][j]
-        if corr == 1:
+        if abs(abs(corr) - 1.0) <= 1e-8:
             logging.warning('Parameters are 100%% correlated: %s, %s', parx.name, pary.name)
-            corr = self.max_corr_2D
+            corr = np.sign(corr) * self.max_corr_2D
 
         logging.debug('Doing 2D: %s - %s', parx.name, pary.name)
         logging.debug('sample x_err, y_err, correlation: %s, %s, %s', parx.err, pary.err, corr)