Limit functions allowed in student answers

classes/local/answer_parser.php

@@ -177,10 +177,10 @@ private function is_acceptable_numeric(): bool {
     /**
      * Check whether the given answer contains only valid tokens for the answer type NUMERICAL_FORMULA, i. e.
      * - numerical expression
-     * - plus functions: sin, cos, tan, asin, acos, atan, atan2, sinh, cosh, tanh, asinh, acosh, atanh
-     * - plus functions: sqrt, exp, log, log10, ln
+     * - plus functions: sin, cos, tan, asin, acos, atan (but not atan2), sinh, cosh, tanh, asinh, acosh, atanh
+     * - plus functions: sqrt, exp, log10, ln, lg (but not log)
      * - plus functions: abs, ceil, floor
-     * - plus functions: fact, ncr, npr
+     * - plus functions: fact
      * - no variables
      *
      * @return bool
@@ -222,9 +222,14 @@ private function is_acceptable_algebraic_formula(bool $fornumericalformula = fal
         $answertokens = $this->statements[0]->body;
 
         // Iterate over all tokens. If we find a FUNCTION token, we check whether it is in the white list.
+        // Note: We currently restrict the list of allowed functions to functions with only one argument.
+        // That assures full backwards compatibility, without limiting our future possibilities w.r.t. the
+        // usage of the comma as a decimal separator. We do not currently allow the 'log' function (which
+        // would mean the natural logarithm), because it was not allowed in earlier versions, creates ambiguity
+        // and would accept two arguments.
         $functionwhitelist = [
-            'sin', 'cos', 'tan', 'asin', 'acos', 'atan', 'atan2', 'sinh', 'cosh', 'tanh', 'asinh', 'acosh', 'atanh',
-            'sqrt', 'exp', 'log', 'log10', 'ln', 'abs', 'ceil', 'floor', 'fact', 'ncr', 'npr',
+            'sin', 'cos', 'tan', 'asin', 'acos', 'atan', 'sinh', 'cosh', 'tanh', 'asinh', 'acosh', 'atanh',
+            'sqrt', 'exp', 'log10', 'ln', 'lg', 'abs', 'ceil', 'floor', 'fact',
         ];
         $operatorwhitelist = ['+', '_', '-', '/', '*', '**', '^', '%'];
         foreach ($answertokens as $token) {

classes/local/functions.php

@@ -76,6 +76,7 @@ class functions {
         'join' => [2, INF],
         'lcm' => [2, 2],
         'len' => [1, 1],
+        'lg' => [1, 1],
         'ln' => [1, 1],
         'map' => [2, 3],
         'modinv' => [2, 2],
@@ -1089,6 +1090,19 @@ public static function binomialcdf(float $n, float $p, float $x): float {
         return $res;
     }
 
+    /**
+     * Calculate the common logarithm of a number.
+     *
+     * @param float $x number
+     * @return float
+     */
+    public static function lg(float $x): float {
+        if ($x <= 0) {
+            self::die('error_func_positive', 'lg()');
+        }
+        return log10($x);
+    }
+
     /**
      * Calculate the natural logarithm of a number.
      *

script/formatcheck.js

@@ -51,13 +51,13 @@ function formulas_format_check() {
 
     // The list of allowable (single parameter) function and their evaluation replacement.
     var funclist = {'sin': 1, 'cos': 1, 'tan': 1, 'asin': 1, 'acos': 1, 'atan': 1, 'exp': 1,
-        'log10': 1, 'ln': 1, 'sqrt': 1, 'abs': 1, 'ceil': 1, 'floor': 1, 'fact': 1};
+        'lg': 1, 'log10': 1, 'ln': 1, 'sqrt': 1, 'abs': 1, 'ceil': 1, 'floor': 1, 'fact': 1};
 
     // The replacement list used when preform trial evaluation, note it is not the same as dispreplacelist
     // Replace 'fact' (factorial) by 'abs', because JS does not have a factorial function and
     // therefore, an expression containing fact() will always be considered as invalid. We use abs(),
     // because we just need some replacement function and are not interested in the actual result.
-    var evalreplacelist = {'ln': 'log', 'log10': '(1./log(10.))*log', 'fact': 'abs'}; // Natural log and log with base 10, no log allowed to avoid ambiguity.
+    var evalreplacelist = {'lg': 'log10', 'ln': 'log', 'log10': '(1./log(10.))*log', 'fact': 'abs'}; // Natural log and log with base 10, no log allowed to avoid ambiguity.
 
     // The replacement list used when the formula is displayed on the screen.
     var dispreplacelist = {'log10': 'log<sub>10</sub>', '3.14159265358979323846': '<i>π</i>'};
@@ -741,6 +741,7 @@ function formulas_format_check() {
             ['numerical_formula', true, '3+4^-9'],
             ['numerical_formula', true, '3+exp(4+5)^-sin(6+7)'],
             ['numerical_formula', true, '1+ln(3)'],
+            ['numerical_formula', true, '1+lg(3)'],
             ['numerical_formula', true, '1+log10(3)'],
             ['numerical_formula', true, 'pi'],
             ['numerical_formula', false, 'pi()'],
@@ -780,7 +781,7 @@ function formulas_format_check() {
             ['algebraic_formula', true, 'a+b^(c^d)+f'],
             ['algebraic_formula', true, 'a+(b^c)^d+f'],
             ['algebraic_formula', true, 'a+b^c^-d'],
-            ['algebraic_formula', true, '1+ln(a)+log10(b)'],
+            ['algebraic_formula', true, '1+ln(a)+log10(b)+lg(c)'],
             ['algebraic_formula', true, 'asin(w t)'],   // arcsin(w*t)
             ['algebraic_formula', true, 'a sin(w t)+ b cos(w t)'], // a*sin(w*t) + b*cos(w*t)
             ['algebraic_formula', true, '2 (3) a sin(b)^c - (sin(x+y)+x^y)^-sin(z)c tan(z)(x^2)'],

tests/answer_parser_test.php

@@ -128,7 +128,7 @@ public static function provide_algebraic_formulas(): array {
             [qtype_formulas::ANSWER_TYPE_ALGEBRAIC, 'a+b^(c^d)+f'],
             [qtype_formulas::ANSWER_TYPE_ALGEBRAIC, 'a+(b^c)^d+f'],
             [qtype_formulas::ANSWER_TYPE_ALGEBRAIC, 'a+b^c^-d'],
-            [qtype_formulas::ANSWER_TYPE_ALGEBRAIC, '1+ln(a)+log10(b)'],
+            [qtype_formulas::ANSWER_TYPE_ALGEBRAIC, '1+ln(a)+log10(b)+lg(c)'],
             [qtype_formulas::ANSWER_TYPE_ALGEBRAIC, 'asin(w t)'],
             [qtype_formulas::ANSWER_TYPE_ALGEBRAIC, 'a sin(w t)+ b cos(w t)'],
             [qtype_formulas::ANSWER_TYPE_ALGEBRAIC, '2 (3) a sin(b)^c - (sin(x+y)+x^y)^-sin(z)c tan(z)(x^2)'],

tests/evaluator_test.php

@@ -359,6 +359,7 @@ public static function provide_expressions_with_functions(): array {
             'several arguments' => ['foo-bar-test', 'a="foo"; b="bar"; c="test"; join("-", a, b, c)'],
             'function with array' => [6, 'sum([1,2,3])'],
             'natural logarithm' => [2.708050201102210065996, 'ln(15)'],
+            'common logarithm' => [3, 'lg(1000)'],
             'nested function' => [-0.35473297204849, 'sin(4) + exp(cos(4+5))'],
         ];
     }
@@ -1499,6 +1500,14 @@ public static function provide_invalid_assignments(): array {
                 'ln() expects its argument to be a positive number.',
                 'x=ln(0)',
             ],
+            'undefined common logarithm' => [
+                'lg() expects its argument to be a positive number.',
+                'x=lg(-5)',
+            ],
+            'undefined common logarithm, 2' => [
+                'lg() expects its argument to be a positive number.',
+                'x=lg(0)',
+            ],
             'closing parenthesis when not opened' => [
                 "1:7:Unbalanced parenthesis, stray ')' found.",
                 's=fill);',
@@ -1990,7 +1999,7 @@ public static function provide_algebraic_formulas(): array {
             [true, 'a+b^(c^d)+f'],
             [true, 'a+(b^c)^d+f'],
             [true, 'a+b^c^-d'],
-            [true, '1+ln(a)+log10(b)'],
+            [true, '1+ln(a)+log10(b)+lg(c)'],
             [true, 'asin(w t / 100)'],
             [true, 'a sin(w t)+ b cos(w t)'],
             [true, '2 (3) a sin(b)^c - (sin(x+y)+x^y)^-sin(z)c tan(z)(x^2)'],

tests/functions_test.php

@@ -914,6 +914,9 @@ public static function provide_algebraic_numerical_function_invocations(): array
             [true, 'a=log10(0.5);'],
             [false, 'a=log10();'],
             [false, 'a=log10(1, 2);'],
+            [true, 'a=lg(0.5);'],
+            [false, 'a=lg();'],
+            [false, 'a=lg(1, 2);'],
             [true, 'a=log1p(0.5);'],
             [false, 'a=log1p();'],
             [false, 'a=log1p(1, 2);'],