Add packages/math/math.md

packages/math/math.md

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+# Math library
+
+This library adds extra math functions to Ground. Unlike the official math library, all these features are coded in pure Ground.
+
+Please note that you cannot copy a single function from the package, as some functions rely on other functions in the library.
+
+## Functions
+
+### fun -double !sin -double &input
+
+Gets the sin of input.
+
+### fun -double !cos -double &input
+
+Gets the cos of input.
+
+### fun -double !tan -double &input
+
+Gets the tan of input.
+
+### fun -double !intexp -double &base -int &power
+
+Returns base^power, for positive integer values of power. Returns 1 if power is non-positive (and thus is inaccurate for negative values of power).
+
+### fun -double !sqrt -double &input
+
+Returns the positive value *x* that satisfies x^2 = input. Throws an error if input is negative.
+
+### fun -double !mod -double &in -double &modulus
+
+Returns *n* such that *n* is congruent to the input modulo $modulus, where *n* is at least 0 and less than $modulus.
+
+### fun -double !random -int &seed
+
+Gets a random double in the domain [0,1), using a LCG. A seed is required.
+
+### fun -double !pi
+
+Returns pi to the maximum accuracy that doubles can store.
+
+### fun -double !itod -int &input
+
+Returns the input as a double.
+
+### fun -int !dtoi -double &input
+
+Returns the input as an integer.