# John D'Errico

### Retired

A retired applied mathematician, consultant, sometime mechanical engineer, numerical analyst, woodworker, bridge player. Please DON'T contact me, as too many students then decide I am their personal consultant if I allow it. I won't do consulting by mail.

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**Feeds**

Solved

Divisible by 2

This is the first problem in a set of "divisible by x" problems. You will be provided a number as a string and the function you ...

3 years ago

Solved

Edges of a n-dimensional Hypercube

Return the number of edges on an <http://en.wikipedia.org/wiki/Hypercube _n_-dimensional hypercube> (with an integer n ≥ 0). ...

6 years ago

Solved

Dots in a Circle

Return how many integer grid points there are inside a circle of radius _r_ centred at (0,0) (including points on the edge). ...

6 years ago

Solved

The average of the second largest values

Given a matrix, find the average of the second largest values in each row. The same value does not exist on a row. Example: ...

6 years ago

Solved

Fibonacci-Sum of Squares

Given the Fibonacci sequence defined by the following recursive relation, * F_n = F_(n-1) + F_(n-2) * where F_0 = 0 and F_1 ...

6 years ago

Solved

Volume of a Simplex

Return the volume of a <http://en.wikipedia.org/wiki/Simplex regular _n_-simplex> with a unit side length. Results are up to...

6 years ago

Solved

Volume difference between Ellipsoid and Sphere

Given an ellipsoid of semi principal axis (a,b,c) find the volume of the difference between this ellipsoid and the sphere with...

6 years ago

Solved

Perimeter

Given a sequence of points forming a closed path (first and last points are coincident) return the perimeter value. For example...

6 years ago

Solved

Return the Fibonacci Sequence

Write a code which returns the Fibonacci Sequence such that the largest value in the sequence is less than the input integer N. ...

6 years ago

Solved

Find nearest prime number less than input number

Find nearest prime number less than input number. For example: if the input number is 125, then the nearest prime number whi...

6 years ago

Solved

sum of non-primes

The sum of the non-primes no larger than 10 is 1+4+6+8+9+10=38 Find the sum of all the positive non-prime integers that do no...

6 years ago

Solved

Extra safe primes

Did you know that the number 5 is the first safe prime? A safe prime is a prime number that can be expressed as 2p+1, where p is...

6 years ago

Solved

Pernicious Anniversary Problem

Since Cody is 5 years old, it's pernicious. A <http://rosettacode.org/wiki/Pernicious_numbers Pernicious number> is an integer w...

6 years ago

Solved

Get linearly independent vectors of given matrix.

Get a set of linearly independent vectors from the rows of a given matrix. Example matrix=[ 3 -1 0 0 ; ...

7 years ago

Problem

Euclidean distance from a point to a polynomial

A not uncommon problem in the area of computational geometry is to find the closest point to a straight line from a given point,...

7 years ago | 3 | 28 solvers

Solved

For given xx,x, y vectors build spline of x and y and find yy values for xx vector.

For given xx,x, y vectors build spline of x and y and find yy values for xx vector. Example x = [ 1.0000 1.5000 2.00...

7 years ago

Solved

What's size of TV?

Many people buy TV. Usually they ask about diagonal. But also important are width and height. Let's assume that all TV have rati...

7 years ago

Problem

Euclidean inter-point distance matrix

The Euclidean distance between two points in a p-dimensional space is a really common thing to compute in the field of computati...

7 years ago | 1 | 24 solvers

Solved

Prime number removal

remove all prime numbers from the input e.g. input = 1 2 3 4 5 6 7 8 9 10 11 12 ...

7 years ago

Solved

Determine the roots of a cubic equation

Given the coefficients a, b, c, and d of a cubic equation, a*x^3 + b*x^2 + c*x + d = 0, determine its roots.

7 years ago

Solved

Roots of a quadratic equation.

Calculate the roots of a quadratic equation, given coefficients a, b, and c, for the equation a*x^2 + b*x + c = 0.

7 years ago

Solved

Sum of digits of powers of 2

Given n, first, calculate the number 2^n. Then, sum the digits that comprise that number. For example: Input: n = 7 2^n = ...

7 years ago

Problem

Simpsons's rule (but not Homer Simpson)

I wonder what Homer Simpson would have thought of Simpson's rule? Somehow I doubt his thoughts would have included the phrase Ne...

7 years ago | 4 | 36 solvers

Solved

Right and wrong

Given a vector of lengths [a b c], determines whether a triangle with those sides lengths is a right triangle: <http://en.wikipe...

8 years ago

Solved

Make a Palindrome Number

Some numbers like 323 are palindromes. Other numbers like 124 are not. But look what happens when we add that number to a revers...

8 years ago

Solved

Solve the Sudoku Row

*Description* A simple yet tedious task occurs near the end of most Sudoku-solving algorithms, computerized or manual. The ta...

8 years ago

Solved

Sums of cubes and squares of sums

Given the positive integers 1:n, can you: 1. Compute twice the sum of the cubes of those numbers. 2. Subtract the square...

8 years ago

Problem

Sums of cubes and squares of sums

Given the positive integers 1:n, can you: 1. Compute twice the sum of the cubes of those numbers. 2. Subtract the square...

8 years ago | 9 | 247 solvers

Solved

Project Euler: Problem 6, Natural numbers, squares and sums.

The sum of the squares of the first ten natural numbers is, 1^2 + 2^2 + ... + 10^2 = 385 The square of the sum of the first ...

8 years ago

Solved

Determine Whether an array is empty

Input a matrix x, output y is TRUE if x is empty, otherwise FALSE.

8 years ago