
February 9th, 2011, 05:08 AM
#1
maximum, minimum and average of a matrix?
std::vector<std::vector<unsigned long> > matrix(15); // 15 rows
typedef std::vector<std::vector<unsigned long> >::iterator it_type;
it_type row = matrix.begin();
for (int w=0;w<10;w++)
{
//some lines of code
unsigned long num = x.to_ulong();
cout <<"Decimal form is: " << num<< end;
// if we've hit 15 items in the current row (i.e. 15 columns), then shift to the next row
if (row>size() == 15)
++row;
// add this to the next column in the current row
row>push_back(num);
}
// resize the last row
row>resize(15); // this will ensure that there are 15 columns in the last row
for(size_t i=0; i < matrix.size(); ++i)
{
for(size_t j=0; j < matrix[i].size(); ++j)
cout << matrix[i][j] << " ";
cout << endl;
}
Now I want to find maximum, minimum and average of this matrix. What shall I do?

February 9th, 2011, 05:13 AM
#2
Re: maximum, minimum and average of a matrix?
It would be a lot easier to achieve if you were to wrap a 1D vector in a Matrix class.
See http://www.parashift.com/c++faqlit...html#faq13.10
"It doesn't matter how beautiful your theory is, it doesn't matter how smart you are. If it doesn't agree with experiment, it's wrong."
Richard P. Feynman

February 9th, 2011, 05:16 AM
#3
Re: maximum, minimum and average of a matrix?

February 9th, 2011, 06:00 AM
#4
Re: maximum, minimum and average of a matrix?
A simple example.
Code:
#include <vector>
#include <algorithm>
class matrix
{
public:
matrix()
: n_columns(0),
n_rows(0)
{
}
matrix(int columns, int rows)
: n_columns(columns),
n_rows(rows),
data(columns * rows)
{
}
int operator ()(int row, int column)
{
return data[column + (row * n_columns)];
}
std::vector<int>::iterator begin()
{
return data.begin();
}
std::vector<int>::iterator end()
{
return data.end();
}
private:
std::vector<int> data;
int n_columns;
int n_rows;
};
int main()
{
matrix m(10, 20);
// Fill the matrix here.
// Find the maximum value in the matrix.
int maximum = *std::max_element(m.begin(), m.end());
// Get element at 4,6
int value = m(4, 6);
}
"It doesn't matter how beautiful your theory is, it doesn't matter how smart you are. If it doesn't agree with experiment, it's wrong."
Richard P. Feynman

February 9th, 2011, 07:06 AM
#5
Re: maximum, minimum and average of a matrix?
thanks. but if i implement it this way, it gives lots of errors.

February 9th, 2011, 07:19 AM
#6
Re: maximum, minimum and average of a matrix?
"It doesn't matter how beautiful your theory is, it doesn't matter how smart you are. If it doesn't agree with experiment, it's wrong."
Richard P. Feynman

February 9th, 2011, 07:55 AM
#7
Re: maximum, minimum and average of a matrix?
Originally Posted by JohnW@Wessex
What errors?
I couldn't find any errors, however:
Originally Posted by JohnW@Wessex
A simple example.
Code:
class matrix
{
matrix(int columns, int rows)
: n_columns(columns),
n_rows(rows),
data(columns * rows)
{
}
...
private:
std::vector<int> data;
int n_columns;
int n_rows;
};
You might want to be careful with your order of initialization.
Is your question related to IO?
Read this C++ FAQ article at parashift by Marshall Cline. In particular points 16.
It will explain how to correctly deal with IO, how to validate input, and why you shouldn't count on "while(!in.eof())". And it always makes for excellent reading.

February 9th, 2011, 08:27 AM
#8
Re: maximum, minimum and average of a matrix?
Originally Posted by monarch_dodra
You might want to be careful with your order of initialization.
The constructor initialises all of the members with the constructor parameters, so everything should be fine. Now if I'd used 'n_rows' & 'n_columns' to initialise 'data', that would be different.
I avoid dependencies of member declaration; it's too open to accidental error.
"It doesn't matter how beautiful your theory is, it doesn't matter how smart you are. If it doesn't agree with experiment, it's wrong."
Richard P. Feynman
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