><code>int</code> <strong><code>is_inf</code></strong><code>(real x)</code><br>
Return 1 if x is infinite (positive or negative) and 0 otherwise.</p>
<!-- int; is_nan; (real x); -->
<p></p>
<p><code>int</code> <strong><code>is_nan</code></strong><code>(real x)</code><br>
Return 1 if x is NaN and 0 otherwise.</p>
<p>Care must be taken because both of these indicator functions are
step-like and thus can cause discontinuities in gradients when applied
to parameters; see section <a href="step-functions.html#ste