How to multiply a matrix by a vector

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How to multiply a matrix by a vector

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#1 by (0 votes)

-1

Good evening I am finishing a program for the faculty and I am missing a part of the code to multiply a matrix by a vector, in this case it would be the multiplication of the quantity vector [i] [j] * prices [j]. (In the code is an attempt at multiplication but it does not work), if someone can give me some help, I would be very grateful, thank you very much. Here I leave the code walking.

#include<iostream>
using namespace std;

int main()
{
    int cantidad[3][5], precios[5], recaudacion[5], i, j, total;
    string nombresArticulos[5];

    //ingreso e imprime los nombres de los articulos
    i=0;
    while(i<5)
    {
        cout<<"Ingrese los nombres de los articulos:"<<endl;
        cin>>nombresArticulos[i];
        i++;
    }

    for(i=0; i<5; i++)
    {
        cout<<nombresArticulos[i]<<endl;
    }

    //guarda los precios de cada articulo
    for(j=0; j<5;j++)
    {
        cout<<"Ingrese precios de cada articulo"<<endl;
        cin>>precios[5];

    }

    //ingreso de la cantidad de articulos vendidos por cada vendedor
    cout<<"Ingrese la cantidad de articulos vendidos por cada vendedor: "<<endl;
    for(i=0; i<3; i++)
    {
        for(j=0; j<5; j++)
        {
            cout<<"Vendedor: "<<i+1<<" "<<"Articulo: "<<j+1<<endl;
            cin>>cantidad[i][j];
        }

    }

    for(i=0; i<3; i++)
    {
         for(j=0; j<5; j++)
        {
            //cout<<"Vendedor: "<<i+1<<" "<<"Articulo: "<<j+1<<endl;
            cout<<cantidad[i][j]<<endl;
        }

    }

    //cantidad de dinero recaudado por cada vendedor
    for(i=0; i<3; i++)
    {
        for(j=0; j<5; j++)
        {
            recaudacion[j]=cantidad[i][j]*precios[j];
        }

    }

    for(j=0; j<5; j++)
    {
        cout<<recaudacion[j]<<endl;
    }

}

c++11

asked by Cpp 30.09.2018 в 06:17

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1 answer

Exception when calling a Thread from another class Error creating the model class

score 0 · Answer 1

You're supposed to be calculating the money raised by each vendor. And since in your program you define three sellers, the vector resultado must have 3 elements ... not 5.

int recaudacion[3];

Well, at this point, your exercise is solved by applying the theory of matrix multiplication. That is, given a 3x5 matrix and a 5x1 matrix, we will obtain a 3x1 matrix. Matrix multiplication theory here .

When multiplying matrices, in each cell of the result matrix not a single product is stored, but a sum of products ... it is important not to forget to initialize the variables:

for(int i=0; i<3; i++)
{
  recaudacion[i] = 0;
  for(int j=0; j<5; j++)
  {
    recaudacion[i] += cantidad[i][j]*precios[j];
  }
}

And, please, do not declare all the variables at the start of the function. Try to reduce your life to the fullest. You will get more readable programs with fewer errors.