added documentation to fpEqual on behavior for NaNs/Infs

gtsam/base/Vector.h

@@ -80,9 +80,14 @@ static_assert(
  * Numerically stable function for comparing if floating point values are equal
  * within epsilon tolerance.
  * Used for vector and matrix comparison with C++11 compatible functions.
- * Return true if two numbers are close wrt epsilon.
+ *
+ * If either value is NaN or Inf, we check for both values to be NaN or Inf
+ * respectively for the comparison to be true.
+ * If one is NaN/Inf and the other is not, returns false.
+ *
+ * Return true if two numbers are close wrt tol.
  */
-GTSAM_EXPORT bool fpEqual(double a, double b, double epsilon);
+GTSAM_EXPORT bool fpEqual(double a, double b, double tol);
 
 /**
  * print without optional string, must specify cout yourself