As a result of processing arrays -nan(ind)

Question

0.00/5 (No votes)

See more:

I am writing a program that creates arrays of a given length and manipulates them. You cannot use other libraries.

First, an array M1 of length N is formed, after which an array M2 of length N is formed/2.
In the M1 array, the division by Pi operation is applied to each element, followed by elevation to the third power.
Then, in the M2 array, each element is alternately added to the previous one, and the tangent modulus operation is applied to the result of addition.
After that, exponentiation is applied to all elements of the M1 and M2 array with the same indexes and the resulting array is sorted by dwarf sorting.
And at the end, the sum of the sines of the elements of the M2 array is calculated, which, when divided by the minimum non-zero element of the M2 array, give an even number.
The problem is that the result X gives is -nan(ind). I can't figure out exactly where the error is.

C

#include <stdio.h>
#include <math.h>
#include <stdlib.h>
 
const int A = 441;
const double PI = 3.1415926535897931159979635;
 
inline void dwarf_sort(double* array, int size) {
    size_t i = 1;
    while (i < size) {
        if (i == 0) {
            i = 1;
        }
        if (array[i - 1] <= array[i]) {
            ++i;
        }
        else
        {
            long tmp = array[i];
            array[i] = array[i - 1];
            array[i - 1] = tmp;
            --i;
        }
    }
}
 
inline double reduce(double* array, int size) {
 
    size_t i;
    double min = RAND_MAX, sum = 0;
 
    for (i = 0; i < size; ++i) {
        if (array[i] < min && array[i] != 0) {
            min = array[i];
        }
    }
 
    for (i = 0; i < size; ++i) {
        if ((int)(array[i] / min) % 2 == 0) {
            sum += sin(array[i]);
        }
    }
    return sum;
}
 
int main(int argc, char* argv[])
{
    int i, N, j;
    double* M1 = NULL, * M2 = NULL, * M2_copy = NULL;
    double X;
    unsigned int seed = 0;
 
    N = atoi(argv[1]);
    M1 = malloc(N * sizeof(double));
    M2 = malloc(N / 2 * sizeof(double));
    M2_copy = malloc(N / 2 * sizeof(double));
 
    for (i = 0; i < 100; i++) 
    {
        seed = i;
        srand(i); 
        
        /*generate*/
        for (j = 0; j < N; ++j) {
            M1[j] = (rand_r(&seed) % A) + 1;
        }
 
        for (j = 0; j < N / 2; ++j) {
            M2[j] = (rand_r(&seed) % (10 * A)) + 1;
        }
 
        /*map*/
        for (j = 0; j < N; ++j)
        {
            M1[j] = pow(M1[j] / PI, 3);
        }
 
        for (j = 0; j < N / 2; ++j) {
            M2_copy[j] = M2[j];
        }
 
        M2[0] = fabs(tan(M2_copy[0]));
        for (j = 0; j < N / 2; ++j) {
            M2[j] = fabs(tan(M2[j] + M2_copy[j]));
        }
 
        /*merge*/
        for (j = 0; j < N / 2; ++j) {
            M2[j] = pow(M1[j], M2[j]);
        }
 
        /*sort*/
        dwarf_sort(M2, N / 2);
 
        /*sort*/
        X = reduce(M2, N / 2);
    }
    
    printf("\nN=%d.\n", N); 
    printf("X=%f\n", X);
    return 0;
}

What I have tried:

Knowledgeable people, does anyone see where my mistake is? I think I'm putting the wrong data types to the variables, but I still can't solve the problem.

Posted 31-Mar-22 2:14am

Dmitrii Shurygin

Updated 31-Mar-22 4:23am

Add a Solution

Comments

Richard MacCutchan 31-Mar-22 8:51am

In your dwarf_sort function you have the following:

            long tmp = array[i];
            array[i] = array[i - 1];
            array[i - 1] = tmp;

Did you mean to convert a double value to a long integer?

Dmitrii Shurygin 31-Mar-22 8:55am

It was my mistake, I changed long to double, but it didn't solve the problem.

Richard MacCutchan 31-Mar-22 9:02am

You need to use the debugger, or add a lot of print statements to show what happens when you run it. It is too complicated to solve just by reading the code.

Dmitrii Shurygin 31-Mar-22 9:06am

I think I found an error at the merge stage. After exponentiation, I get huge numbers that can go beyond double. But I don't know yet how to raise it to a power and not go beyond double, so as not to get nan.

2 solutions

Add a Solution

Add your solution here

Treat my content as plain text, not as HTML

Preview 0

…

Existing Members

Sign in to your account

...or Join us

Download, Vote, Comment, Publish.

Your Email
Password
Forgot your password?

Your Email
This email is in use. Do you need your password?
Optional Password

I have read and agree to the Terms of Service and Privacy Policy
Please subscribe me to the CodeProject newsletters

When answering a question please:

Read the question carefully.
Understand that English isn't everyone's first language so be lenient of bad spelling and grammar.
If a question is poorly phrased then either ask for clarification, ignore it, or edit the question and fix the problem. Insults are not welcome.
Don't tell someone to read the manual. Chances are they have and don't get it. Provide an answer or move on to the next question.

Let's work to help developers, not make them feel stupid.

This content, along with any associated source code and files, is licensed under The Code Project Open License (CPOL)

OriginalGriff · Answer 1 · 2022-03-31T02:46:00

Compiling does not mean your code is right! :laugh:
Think of the development process as writing an email: compiling successfully means that you wrote the email in the right language - English, rather than German for example - not that the email contained the message you wanted to send.

So now you enter the second stage of development (in reality it's the fourth or fifth, but you'll come to the earlier stages later): Testing and Debugging.

Start by looking at what it does do, and how that differs from what you wanted. This is important, because it give you information as to why it's doing it. For example, if a program is intended to let the user enter a number and it doubles it and prints the answer, then if the input / output was like this:

Input   Expected output    Actual output
  1            2                 1
  2            4                 4
  3            6                 9
  4            8                16

Then it's fairly obvious that the problem is with the bit which doubles it - it's not adding itself to itself, or multiplying it by 2, it's multiplying it by itself and returning the square of the input.
So with that, you can look at the code and it's obvious that it's somewhere here:

C

int Double(int value)
   {
   return value * value;
   }

Once you have an idea what might be going wrong, start using the debugger to find out why. Put a breakpoint on the first line of the method, and run your app. When it reaches the breakpoint, the debugger will stop, and hand control over to you. You can now run your code line-by-line (called "single stepping") and look at (or even change) variable contents as necessary (heck, you can even change the code and try again if you need to).
Think about what each line in the code should do before you execute it, and compare that to what it actually did when you use the "Step over" button to execute each line in turn. Did it do what you expect? If so, move on to the next line.
If not, why not? How does it differ?
Hopefully, that should help you locate which part of that code has a problem, and what the problem is.
This is a skill, and it's one which is well worth developing as it helps you in the real world as well as in development. And like all skills, it only improves by use!

KarstenK · Answer 2 · 2022-03-31T04:23:00

Solution 2

You must learn to use the debugger to find the error. Best is often to provide some sample data for each function and run it. When finding some bugs step into it.

Nan is normally the result of uninitialized memory, so your code hasnt touch this variable. Try to set i to 3 to start it.

Posted 31-Mar-22 4:23am

KarstenK