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i have file pointer and i think an array, i just dnt know what number to use in the brackets.
the i have to filepoint this file to my program.
inputf.dat which is the following matrix or set of numbers
1.0 1.0 -4.0 -0.5
-2.0 1.5 1.0 2.1
-1.1 0.7 -2.5 4.2
2.4 0.3 0.4 -1.9
0.8 1.2 -0.9 -0.5
input_1=fopen("inputf.dat", "r")
if(input_1==NULL) exit(1);
int m=0; j, i, n;
char line[?]; <-this is my question. what number do i type here?
by the way if this is what im suppose to do.
By using a pointer to pointer **A and the function calloc()
allocate the memory for the 4x4 matrix A[][].
By using a pointer *x and the function malloc()
allocate the memory for the 4-dimensional vector x[].
Read the components of A and x from the given input file inputf.dat
(which is in the public directory; you need to copy it into your directory).
The last line of the input file contains the components of x. The rows of
matrix A are the first four lines of the input file. Print the components
of A[][] and x[]
all i need to know is what number belongs in the bracket
The first thing you need to do is read the data from the file.
What is the purpose of:
Code:char line[?];
the purpose is to input the data into my program right?
Well, what do you suppose the maximum length of a line will be from your file? That array has to be large enough to hold that length.
And if you're asking these questions, this assignment probably exceeds your capabilities.
That does not happen automatically. Using C++, you could do that with an ifstream and getline().Quote:
Originally Posted by rafacnsoccer
getline - C++ Reference
Or you could use fopen and fgets from <cstdio>
fgets - C++ Reference
which would use a C string such as char line[]. Then you have to extract the data from the line into the matrix.
First, I would just write a short routine to open the file and print it all out line by line, then close it. When that works smoothly, you can decide how to extract the data.
well this is the other part i didnt add hopefully this helps
char line[?];
double **A, *x;
A=(double **)calloc(4,sizeof(double *));
for(i=0;i<4;i++)
A[i]=(double *)calloc(4 ,sizeof(double));
x=(double *)malloc(4*sizeof(double));
Okay, so probably 64 bytes is enough for the line, so the next bit starts:
Code:while (fgets(line,64,input_1)) cout << line;
okay that helps thanks, i finished the rest but the thing is now, i do not know how to write the program for the transpose A_s. which the formula used ismatrix A_s=(A+A_t)/2
the normal matrix i obtained with this
insertand then itsCode:char line[64];
double **A, *x;
A=(double **)calloc(4,sizeof(double *));
for(i=0;i<4;i++)
A[i]=(double *)calloc(4 ,sizeof(double));
x=(double *)malloc(4*sizeof(double));
while(fgets(line,64,input_1,) != NULL
{
if(k==4) sscanf(line, "%lf %lf %lf %lf", &x[0],&x[1],&x[2],&x[3]);
else
{
sscanf(line, "%lf %lf %lf %lf", &A[m][0],&A[m][1],&A[m][2],&A[m][3]);
}
m++;
}
printf("Matrix A is:");
printf("\n\n");
for(q=0;q<4;q++)
printf("%6.3f ",A[0][q]);
printf("\n");
for(j=0;j<4;j++)
printf("%6.3f ",A[1][q]);
printf("\n");
for(j=0;j<4;j++)
printf("%6.3f ",A[2][q]);
printf("\n");
for(j=0;j<4;j++)
printf("%6.3f ",A[3][q]);
printf("\n\n");
printf("Vector x is:");
printf("\n\n");
printf(" x[] = ");
for(j=0;j<4;j++)
printf("%6.3f ",x[q]);
printf("\n\n");
smatrix(A,x,n);
here is where i dnt know how to make it transpose
am i just suppose to switch A[#][q] to [q]A[#]
Let's make one thing clear: what are you using? C or C++? We can't have both language solutions floating around here...
the class is called mae9 c/c++
Again, what language are you using? What do you INTEND to use?
we are using c++
Barney S. doesn't like the term "c/c++" :p If you are supposed to be using C++, you have mostly been using vanilla C so far. If that matters you will want to use an fstream instead of cstdio to read the file.Quote:
Originally Posted by rafacnsoccer
Anyway, I'm not sure what you want to do now, you want to create a second matrix by applying some formula to the first one?
Then I suggest you start writing C++ code or converting to C. This is all C.
okay when if its okay with u ill write post the instructions so it be clearer than me explaing\
By calling the function smatrix(A,x,n),with n=4,
which you will construct, determine the components of the matrix A_s=(A+A_t)/2, where
A_t stands for the transpose matrix of A, and the components of the
vector y=(A_s*x)/norm_x, where norm_x denotes the norm (length) of the vector x.
Print the components of the matrix A_s and the vector y in the main.
Free dinamically allocated memory
oh oops then its c sorry for the mistake, i guess i should have posted this in the other forum
i feel dumb now
It doesn't matter that much, as long as you are sure which way you are suppose to go.Quote:
Originally Posted by rafacnsoccer
I don't know much about math, can you do this on paper? As for this bit:
That means smatrix will either return a **double (a new matrix), or else it could change A in place (if that is feasible). If you don't need to use the original A again, changing in place would be better (but it might be impossible depending on the details of the math part).Quote:
Originally Posted by rafacnsoccer
see i look online and all i find are programs using this type of transpose, which i dnt know if its the same
insertCode:int main()
{
int i,j;
double a[4][5] = {{ 1.00, 2.00, 3.00, 4.00, 5.00},
{ 1.00, 4.00, 9.00, 16.00, 25.00},
{ 1.00, 8.00, 27.00, 64.00,125.00},
{ 1.00, 16.00, 81.00,256.00,625.00}};
double b[5][4];
transpose_matrix(&a[0][0], &b[0][0], 4, 5);
for(j=0;j<4;j++)
{
for(i=0;i<5;i++)
{
printf("%6.2lf ", a[j][i]);
}
printf("\n");
}
printf("--\n");
for(j=0;j<5;j++)
{
for(i=0;i<4;i++)
{
printf("%6.2lf ", b[j][i]);
}
printf("\n");
}
}
yea so i am not too sure how to much on or how to translate this using the file pointer