std::inner_product in C++
Compute cumulative inner product of range
Returns the result of accumulating init with the inner products of the pairs formed by the elements of two ranges starting at first1 and first2.
The two default operations (to add up the result of multiplying the pairs) may be overridden by the arguments binary_op1 and binary_op2.
1. Using default inner_product :
Syntax:
Template : T inner_product (InputIterator1 first1, InputIterator1 last1, InputIterator2 first2, T init); Parameters : first1, last1 Input iterators to the initial and final positions in the first sequence. first2 Input iterator to the initial position in the second sequence. The range starts at first2 and has as many elements as the range above [first1, last1]. init Initial value for the accumulator. Neither operations shall modify any of the elements passed as its arguments. Return Type : The result of accumulating init and the products of all the pairs of elements in the ranges starting at first1 and first2. Time Complexity: O(n) Auxiliary Space: O(n)
CPP
// CPP program to illustrate // std :: inner_product #include <iostream> // std::cout #include <functional> // std::minus, std::divides #include <numeric> // std::inner_product // Custom functions int myaccumulator( int x, int y) { return x - y; } int myproduct( int x, int y) { return x + y; } // Driver code int main() { // The value which is added after // finding inner_product b/w elements int init = 100; int series1[] = { 10, 20, 30 }; int series2[] = { 1, 2, 3 }; int n = sizeof (series1) / sizeof (series1[0]); // Elements in series1 std::cout << "First array contains :" ; for ( int i = 0; i < n; i++) std::cout << " " << series1[i]; std::cout << "\n" ; // Elements in series2 std::cout << "Second array contains :" ; for ( int i = 0; i < n; i++) std::cout << " " << series2[i]; std::cout << "\n\n" ; std::cout << "Using custom functions: " ; std::cout << std::inner_product(series1, series1 + 3, series2, init, myaccumulator, myproduct); std::cout << '\n' ; return 0; } |
First array contains : 10 20 30 Second array contains : 1 2 3 Using default inner_product: 240
2. Using functional operation :
Syntax:
Template : T inner_product (InputIterator1 first1, InputIterator1 last1, InputIterator2 first2, T init, BinaryOperation1 binary_op1, BinaryOperation2 binary_op2); Parameters : first1, last1, first2, init are same as above. binary_op1 Binary operation taking two elements of type T as arguments, and returning the result of an accumulation operation. This can either be a function pointer or a function object. binary_op2 Binary operation taking two elements of type T as arguments, and returning the result of the inner product operation. This can either be a function pointer or a function object. Here binary_op1 and binary_op2 are functional operation. Neither operations shall modify any of the elements passed as its arguments. Return Type : The result of accumulating init and the products of all the pairs of elements in the ranges starting at first1 and first2. Time Complexity: O(n) Auxiliary Space: O(n)
CPP
// CPP program to illustrate // std :: inner_product #include <iostream> // std::cout #include <functional> // std::minus, std::divides #include <numeric> // std::inner_product // Custom functions int myaccumulator( int x, int y) { return x + y; } int myproduct( int x, int y) { return x * y; } // Driver code int main() { // The value which is added after // finding inner_product b/w elements int init = 0; int series1[] = { 1, 2, 3, 4 }; int series2[] = { 10, 20, 30, 40 }; int n = sizeof (series1) / sizeof (series1[0]); // Elements in series1 std::cout << "Array 1 :" ; for ( int i = 0; i < n; i++) std::cout << " " << series1[i]; std::cout << "\n" ; // Elements in series2 std::cout << "Array 2 :" ; for ( int i = 0; i < n; i++) std::cout << " " << series2[i]; std::cout << "\n\n" ; std::cout << "Sum of products : " ; std::cout << std::inner_product(series1, series1 + n, series2, init, myaccumulator, myproduct); std::cout << '\n' ; return 0; } |
First array contains : 10 20 30 Second array contains : 1 2 3 Using functional operations: 70
3. Using custom functions :
Syntax:
Template : T inner_product (InputIterator1 first1, InputIterator1 last1, InputIterator2 first2, T init, BinaryOperation1 binary_op1, BinaryOperation2 binary_op2); Parameters : first1, last1, first2, init are same as above. binary_op1 Binary operation taking two elements of type T as arguments, and returning the result of an accumulation operation. This can either be a function pointer or a function object. binary_op2 Binary operation taking two elements of type T as arguments, and returning the result of the inner product operation. This can either be a function pointer or a function object. Neither operations shall modify any of the elements passed as its arguments. Return Type : The result of accumulating init and the products of all the pairs of elements in the ranges starting at first1 and first2. Time Complexity: O(n) Auxiliary Space: O(n)
CPP
First array contains : 10 20 30 Second array contains : 1 2 3 Using custom functions: 34
NOTE :
By using functional value and custom function, we can perform operation by changing the operator ( or using different functional value) in this STL function.
Possible Application : It returns the result of accumulating init with the inner products of the pair formed by the elements of two ranges starting at first1 and first2.
1. It can be used to find sum of products of i th index of both arrays.
For Example:
Array 1 : 1 2 3 4
Array 2 : 10 20 30 40
Sum of products : 300
Explanation : 1 * 10 + 2 * 20 + 3 * 30 + 4 * 40 = 300
CPP
// CPP program to illustrate // std :: inner_product #include <iostream> // std::cout #include <functional> // std::minus, std::divides #include <numeric> // std::inner_product // Custom functions int myaccumulator( int x, int y) { return x + y; } int myproduct( int x, int y) { return x * y; } // Driver code int main() { // The value which is added after // finding inner_product b/w elements int init = 0; int series1[] = { 1, 2, 3, 4 }; int series2[] = { 10, 20, 30, 40 }; int n = sizeof (series1) / sizeof (series1[0]); // Elements in series1 std::cout << "Array 1 :" ; for ( int i = 0; i < n; i++) std::cout << " " << series1[i]; std::cout << "\n" ; // Elements in series2 std::cout << "Array 2 :" ; for ( int i = 0; i < n; i++) std::cout << " " << series2[i]; std::cout << "\n\n" ; std::cout << "Sum of products : " ; std::cout << std::inner_product(series1, series1 + n, series2, init, myaccumulator, myproduct); std::cout << '\n' ; return 0; } |
Array 1 : 1 2 3 4 Array 2 : 10 20 30 40 Sum of products : 300
We can also find the difference of products, or sum of division, or difference of division and more all by changing the operator.