Use chi2inv (from stats+ML toolbox) or chi2inv_rtb from RTB

update comments

Author: petercorke

plot_ellipse.m

@@ -37,10 +37,11 @@
 % - The ellipse is added to the current plot irrespective of hold status.
 % - Shadow option only valid for ellipsoids.
 % - If a confidence interval is given then E is interpretted as a covariance
-%   matrix and the ellipse size is computed using an approximate inverse 
-%   chi-squared function.
+%   matrix and the ellipse size is computed using an inverse chi-squared function.
+%   This requires CHI2INV in the Statistics and Machine Learning Toolbox or
+%   CHI2INV_RTB from the Robotics Toolbox for MATLAB.
 %
-% See also PLOT_ELLIPSE_INV, PLOT_CIRCLE, PLOT_BOX, PLOT_POLY, CH2INV_RTB.
+% See also PLOT_ELLIPSE_INV, PLOT_CIRCLE, PLOT_BOX, PLOT_POLY, CH2INV.
 
 % Copyright (C) 1993-2019 Peter I. Corke
 %
@@ -89,8 +90,14 @@
     % process the probability
     if isempty(opt.confidence)
         s = 1;
-    else 
-        s = sqrt(chi2inv_rtb(opt.confidence, 2));
+    else
+        if exist('chi2inv') == 2
+            s = sqrt(chi2inv(opt.confidence, 2));
+        elseif exist('chi2inv_rtb') == 2
+            s = sqrt(chi2inv_rtb(opt.confidence, 2));
+        else
+            error('SMTB:missingfunc', 'Requires Stats Toolbox or RTB to be installed');
+        end
     end
 
     if length(arglist) > 0 && isnumeric(arglist{1})

unit_test/plotXTest.m

@@ -261,7 +261,7 @@ function ellipse2d_test(tc)
     plot_ellipse(E, [0 8 0.5], 'edgecolor', 'r', 'fillcolor', 'c', 'alpha', 0.5, 'LineWidth', 3);
     plot_ellipse(E, [4 8], 'b--', 'LineWidth', 3);
     plot_ellipse(E, 'confidence', 0.5);
-
+    
     h = plot_ellipse(E);
     plot_ellipse(E, [1 1], 'alter', h);
     tc.verifyError(@() plot_ellipse(E, 'alter', 7), 'SMTB:plot_ellipse:badarg');