master: pow_op.hpp: fix bug in pow operator.

pow.sh: Test that verifies fix.
coin-or · Mar 19, 2019 · 2196bce · svigerske · Mar 19, 2019 · 2196bce
1 parent a423932
commit 2196bce
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diff --git a/bug/pow.sh b/bug/pow.sh
@@ -55,6 +55,8 @@ int main(int argc, char** argv)
     //
     x[0]  = 0.0;
     y     = f.Forward(0, x);
+    //
+    f.check_for_nan(false);
     w[0]  = 1.0;
     dw    = f.Reverse(1, w);
     //

diff --git a/include/cppad/local/pow_op.hpp b/include/cppad/local/pow_op.hpp
@@ -666,6 +666,15 @@ void reverse_powvp_op(
     reverse_log_op(
         d, i_z, size_t(arg[0]), cap_order, taylor, nc_partial, partial
     );
+
+    // Special case where partial[ i_z + 2 ] != 0 and x <= 0.
+    // In this case partial[i_z] * (1 / x) is zero, but should not be zero.
+    // (This is a subtitle issue related to the azmul operator.)
+    Base zero(0);
+    if( partial[i_z + 2] != zero  )
+    {   if( ! GreaterThanZero( taylor[ size_t(arg[0]) * cap_order ] ) )
+            partial[arg[0]] = numeric_limits<Base>::quiet_NaN();
+    }
 }
 
 } } // END_CPPAD_LOCAL_NAMESPACE