Add Root Function and Product Function

MathKit/MPRootTerm.m

@@ -0,0 +1,44 @@
+//
+//  MPRootTerm.m
+//  MathPad
+//
+//  Created by Kim Wittenburg on 11.01.15.
+//  Copyright (c) 2015 Kim Wittenburg. All rights reserved.
+//
+
+#import "MPRootTerm.h"
+
+#import "MPParsedExpression.h"
+
+
+
+@implementation MPRootTerm
+
+- (NSDecimalNumber *)doEvaluation:(NSError *__autoreleasing *)error
+{
+    MPEvaluateExpression(exponent, 0);
+    MPEvaluateExpression(root, 1);
+    if ([root compare:[NSDecimalNumber zero]] < 0) {
+        // There are no negative roots.
+        if (error) {
+            *error = [NSError errorWithDomain:MPMathKitErrorDomain
+                                         code:101
+                                     userInfo:@{NSLocalizedDescriptionKey: NSLocalizedString(@"The root of a negative number is undefined.", nil)}];
+        }
+        return nil;
+    }
+    if ([exponent isEqualToNumber:@(0)]) {
+        // The C pow function returns 1 for pow(0, 0). Mathematically this should be undefined.
+        if (error) {
+            *error = [NSError errorWithDomain:MPMathKitErrorDomain
+                                         code:101
+                                     userInfo:@{NSLocalizedDescriptionKey: NSLocalizedString(@"The 0th root is undefined.", nil)}];
+        }
+        return nil;
+    }
+    NSDecimalNumber *actualExponent = [[NSDecimalNumber one] decimalNumberByDividingBy:exponent];
+    return [[NSDecimalNumber alloc] initWithDouble:pow(root.doubleValue, actualExponent.doubleValue)];
+
+}
+
+@end