prime


prime, a MATLAB code which counts the number of primes between 1 and N, and is intended as a starting point for a parallel version.

The algorithm is completely naive. For each integer I, it simply checks whether any smaller J evenly divides it. The total amount of work for a given N is thus roughly proportional to 1/2*N^2.

Here are the counts of the number of primes for some selected values of N:
NNumber of Primes
10
104
10025
1,000168
10,0001,229
100,0009,592
1,000,00078,498
10,000,000664,579
100,000,0005,761,455
1,000,000,00050,847,534

The following results were observed for the elapsed time, running on a Macintosh PowerPC G5:
NPiTime
1 0 0.000030
2 1 0.000016
4 2 0.000016
8 4 0.000017
16 6 0.000020
32 11 0.000030
64 18 0.000057
128 31 0.000147
256 54 0.000452
512 97 0.001548
1,024 172 0.005303
2,048 309 0.018660
4,096 564 0.068059
8,192 1,028 0.246378
16,384 1,900 0.914953
32,768 3,512 3.380086
65,536 6,542 12.619071
131,072 12,251 47.412759

NPiTime
5 3 0.000095
50 15 0.000123
500 95 0.003194
5000 669 0.170837
50,000 5,133 13.081281
500,000 41,538 1,076.868061

Usage:

total = prime ( n )
where

Licensing:

The computer code and data files described and made available on this web page are distributed under the GNU LGPL license.

Languages:

prime is available in a C version and a C++ version and a FORTRAN90 version and a MATLAB version and a Python version.

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prime_test

prime_plot a MATLAB code which displays a box plot of the prime and composite numbers.

quad, a MATLAB code which approximates an integral using a quadrature rule, and is intended as a starting point for parallelization exercises.

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Source Code:


Last revised on 05 March 2019.