Add Root Function and Product Function

MathKit/MPProductFunctionTerm.m

@@ -0,0 +1,40 @@
+//
+//  MPProductFunctionTerm.m
+//  MathPad
+//
+//  Created by Kim Wittenburg on 10.01.15.
+//  Copyright (c) 2015 Kim Wittenburg. All rights reserved.
+//
+
+#import "MPProductFunctionTerm.h"
+
+#import "MPParsedExpression.h"
+
+
+
+@implementation MPProductFunctionTerm
+
+- (NSDecimalNumber *)doEvaluation:(NSError *__autoreleasing *)error
+{
+    MPParsedExpression *startExpression = [self expressionAtIndex:0];
+    NSDecimalNumber *start = [startExpression evaluate:error];
+    ReturnNilIfNil(start);
+    
+    MPEvaluateExpression(target, 1);
+    
+    MPParsedExpression *sumExpression = [self expressionAtIndex:2];
+    NSDecimalNumber *value = [NSDecimalNumber one];
+    for (NSDecimalNumber *current = start;
+         [current compare:target] <= 0;
+         current = [current decimalNumberByAdding:[[NSDecimalNumber alloc] initWithInteger:1]]) {
+        if (![self defineVariable:startExpression.definedVariable value:current error:error]) {
+            return nil;
+        }
+        NSDecimalNumber *currentValue = [sumExpression evaluate:error];
+        ReturnNilIfNil(currentValue);
+        value = [value decimalNumberByMultiplyingBy:currentValue];
+    }
+    return value;
+}
+
+@end