c++ - Determinant calculation error -

- 

#include<iostream.h> #include<conio.h> #include<math.h>  double det (double a[2][2], int size); void form(double a[2][2], int c, int size);  double b[2][2];  double det(double a[2][2], int size) {   if (size==1) {     return a[0][0];   }   else {     double ans = 0.0;     int c;     (c=0;c<size;c++) {       form(a,c,size);       ans += pow(-1.0,(double)c)*det(b,size-1);     }     return ans;   } }  void form(double a[2][2], int c, int size) {   int i,j=0,k,l=0;   (i=0;i<size;i++) {     (j=0;j<size;j++) {       if ((i!=0)&&(j!=c)) {         if (l==size-1) {            k++;            l=0;         }         b[k][l]=a[i][j];         l++;       }     }   } }  int main() {     double mat[2][2] = {{1.0,2.0},{3.0,7.0}};     cout << det(mat,2);     getch();     return 0 ; }

i writing program in c++ calculate determinant of matrix using recursion. know there many better algorithms same. however, have been asked implement one. test case, have used matrix specified in code. when run code, answer of -4 instead of 1. not understand wrong code. please help? in advance.

you made several mistakes in code, use 1 below

#include<iostream> #include<math.h> using namespace std; double det (double a[2][2], int size); void form(double a[2][2], int c, int size); double b[2][2]; double det(double a[2][2], int size) {   if(size==1)     return a[0][0];   else   {     double ans=0.0;     int c;     for(c=0;c<size;c++)     {       form(a,c,size);       ans+=pow(-1.0,(double)c) * a[0][c] * det(b,size-1);     }     return ans;   } } void form(double a[2][2], int c, int size) {   int i,j=0,k = 0,l=0;   for(i=0;i<size;i++)   {     for(j=0;j<size;j++)     {       if((i!=0)&&(j!=c))       {         if(l==size-1)         {            k++;            l=0;         }         b[k][l]=a[i][j];         l++;       }     }   } } int main() {     double mat[2][2]={{1.0,2.0},{3.0,7.0}};     cout<<det(mat,2);     return 0 ; }

this gives 1. mistakes, forget initialize k 0, , forget multiply a[0][c].


Comments

Post a Comment

Popular posts from this blog

c# - How Configure Devart dotConnect for SQLite Code First? -

-
can configure following sample code ? when run following code, error : no entity framework provider found ado.net provider invariant name 'devart.data.sqlite' setting in machine.config <system.data> <dbproviderfactories> <add name="dotconnect sqlite" invariant="devart.data.sqlite" description="devart dotconnect sqlite" type="devart.data.sqlite.sqliteproviderfactory, devart.data.sqlite, version=4.6.287.0, culture=neutral, publickeytoken=09af7300eec23701" /> </dbproviderfactories> </system.data> after add below block code in app.config <?xml version="1.0"?> <configuration>   <configsections> <!-- more information on entity framework configuration, visit http://go.microsoft.com/fwlink/?linkid=237468 --> <section name="entityframework" type="system.data.entity.internal.configfile.entityframeworksection, entit...
Read more

java - Copying object fields -

-
what best way of copying classes when need have 2 independent variables? have simple class: public class myclass { boolean = false; string b= "not empty"; } do need make method : assign(myclass data ) { a= data.a; b= data.b; } is there automatic method copy (duplicate) objects in java? do need make method : pretty close. instead of making method, should make constructor. such constructors called copy constructor , , create them this: myclass(myclass data) { = data.a; b = data.b; } and create copy of instance, use constructor this: myclass obj1 = new myclass(); myclass obj2 = new myclass(obj1); copy constructor can tedious : using copy constructor create deep-copy can tedious, when class has mutable fields. in case, assignment create copy of reference, , not object itself. have create copy of fields (if want deep copy). can go recursive. a better way create deep copy serialize , deserialize object. why not use clone()? ...
Read more

c++ - Clear the memory after returning a vector in a function -

-
i have function processes , stores lot of data in , returns results vector of class. amount of data stored in function tremendous , want clear storage memory of function after finished job. necessary (does function automatically clear memory) or should clear memory function? update: vector<customers> process(char* const *filename, vector<int> id) { vector<customers> list_of_customers; (perform actions) return list_of_customers; } variables defined locally within function automatically released @ end of function scope. destructors objects called, should free memory allocated objects (if objects coded correctly). example of such object std::vector . anything you've allocated new must have corresponding delete release storage. try avoid doing own allocation , use raii instead, i.e. containers or smart pointers.
Read more