Solution 1319950

Submitted on 30 Oct 2017

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3 Comments

3 Comments

Leo Nunnink on 30 Oct 2017

My code works to d=50 and fails on the higher values in the test suite. I think it is a hardware-limited rounding error (?swamping) with very large numbers. When I test eps(fibonacci(100)) on my system, the answer is 6.5 ie my system can not accurately distinguish odd from even at that large a number.

James on 2 Nov 2017

Leo, your theory is correct: The numbers that you're calculating for d>50 are too large to be represented by a 32-bit digit, and won't be calculated correctly for mod(x,2). Think very carefully about the number pattern in the Fibonacci sequence, and see if a pattern emerges.

Mehdi BENSEDDIK on 4 Apr 2019

Indeed, My code works until the d = 50 because it's a large number, so our algorithm is correct we should not worry about it, I think we have succeed in this challenge.

Test Suite

Test	Status	Code Input and Output
1	Pass	d = 14; y_correct = 4; assert(isequal(evenFibo(d),y_correct)) y = 4
2	Pass	d = 20; y_correct = 6; assert(isequal(evenFibo(d),y_correct)) y = 6
3	Pass	d = 50; y_correct = 16; assert(isequal(evenFibo(d),y_correct)) y = 16
4	Fail	d = 100; y_correct = 33; assert(isequal(evenFibo(d),y_correct)) y = 48 Assertion failed.
5	Fail	d = 150; y_correct = 50; assert(isequal(evenFibo(d),y_correct)) y = 98 Assertion failed.
6	Fail	d = 200; y_correct = 66; assert(isequal(evenFibo(d),y_correct)) y = 148 Assertion failed.
7	Fail	d = 500; y_correct = 166; assert(isequal(evenFibo(d),y_correct)) y = 448 Assertion failed.
8	Fail	d = 1000; y_correct = 333; assert(isequal(evenFibo(d),y_correct)) y = 948 Assertion failed.
9	Fail	d = 1e4; y_correct = 3333; assert(isequal(evenFibo(d),y_correct)) y = NaN Assertion failed.
10	Fail	d = 2e4; y_correct = 6666; assert(isequal(evenFibo(d),y_correct)) y = NaN Assertion failed.
11	Fail	d = 3e5; y_correct = 1e5; assert(isequal(evenFibo(d),y_correct)) y = NaN Assertion failed.
12	Fail	d = 6e6; y_correct = 2e6; assert(isequal(evenFibo(d),y_correct)) % % %% % d = 9223372036854775807; % y_correct = 3074457345618258432; % assert(isequal(evenFibo(d),y_correct)) y = NaN Assertion failed.

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