prep for 2023. Fixed many bugs. Added pdf guide

vendor/markbaker/complex/classes/src/functions/csch.php

@@ -0,0 +1,29 @@
+<?php
+
+/**
+ *
+ * Function code for the complex csch() function
+ *
+ * @copyright  Copyright (c) 2013-2018 Mark Baker (https://github.com/MarkBaker/PHPComplex)
+ * @license    https://opensource.org/licenses/MIT    MIT
+ */
+namespace Complex;
+
+/**
+ * Returns the hyperbolic cosecant of a complex number.
+ *
+ * @param     Complex|mixed    $complex    Complex number or a numeric value.
+ * @return    Complex          The hyperbolic cosecant of the complex argument.
+ * @throws    Exception        If argument isn't a valid real or complex number.
+ * @throws    \InvalidArgumentException    If function would result in a division by zero
+ */
+function csch($complex)
+{
+    $complex = Complex::validateComplexArgument($complex);
+
+    if ($complex->getReal() == 0.0 && $complex->getImaginary() == 0.0) {
+        return INF;
+    }
+
+    return inverse(sinh($complex));
+}