Databases
StackOverflow2013
Postsdbo
POBlock Matrix Transpose
 

Note that there are some explanatory texts on larger screens.

plurals
  1. POBlock Matrix Transpose
    primarykey
    data
    text
    <p>I wanted to implement transposition of a matrix by dividing the input matrix into blocks and then transposing them. I referred to the corresponding post <a href="https://stackoverflow.com/questions/5200338/a-cache-efficient-matrix-transpose-program">A Cache Efficient Matrix Transpose Program?</a> and wrote my code like this: </p> <pre><code>#include&lt;iostream&gt; #include&lt;stdlib.h&gt; #define m 4 #include&lt;sys/time.h&gt; #include&lt;time.h&gt; #include&lt;malloc.h&gt; using namespace std; int **a, **b, **c; int count = 0; clock_t t1, t2; int blocksize = 2; int main(){ a = (int **)malloc(m*sizeof(int *)); for(int i = 0;i&lt;m;i++){ a[i] = (int *)malloc(m*sizeof(int)); } b = (int **)malloc(m*sizeof(int *)); for(int i = 0;i&lt;m;i++){ b[i] = (int *)malloc(m*sizeof(int)); } for(int i=0; i&lt;m; i++){ for(int j =0; j&lt;m; j++){ a[i][j]=(2*i)+(3*j); } } for(int i=0; i&lt;m; i++){ for(int j =0; j&lt;m; j++){ cout &lt;&lt; a[i][j] &lt;&lt; "\t"; } cout &lt;&lt; "\n"; } cout &lt;&lt; "\n"; t1 = clock(); // MAIN BLOCK TRANSPOSE CODE for (int i = 0; i &lt; m; i += blocksize) { for (int j = 0; j &lt; m; j += blocksize) { for (int k = i; k &lt; i + blocksize; ++k) { for (int l = j; l &lt; j + blocksize; ++l) { b[k + l*m] = a[l + k*m]; } } } } t2 = clock(); for(int i=0; i&lt;m; i++){ for(int j =0; j&lt;m; j++){ cout &lt;&lt; b[i][j] &lt;&lt; "\t"; } cout &lt;&lt; "\n"; } free(a); free(b); cout &lt;&lt; "\n"; cout &lt;&lt; (double)(t2-t1)/CLOCKS_PER_SEC &lt;&lt; "\n"; return 0; } </code></pre> <p>However, the code is not working as expected. I implemented the code that is said to be working in the corresponding post. Please help if possible. </p> <p>Input Array: </p> <pre><code>0 3 6 9 2 5 8 11 4 7 10 13 6 9 12 15 </code></pre> <p>Expected Output Array:</p> <pre><code>0 2 4 6 3 5 7 9 6 8 10 12 9 11 13 15 </code></pre> <p>Obtained Result: </p> <pre><code>0 3 6 9 Segmentation fault </code></pre>
    singulars
    1. PO
      singulars
      1. PTAnswer
    1. This table or related slice is empty.
    1. PTQuestion
    1. USCommunity
    1. USJustin Carrey
    plurals
    1. PL
      singulars
      1. LTLinked
    1. This table or related slice is empty.
    1. This table or related slice is empty.
    1. PO
      singulars
      1. PTAnswer
    1. VO
      singulars
      1. POBlock Matrix Transpose
      1. This table or related slice is empty.
      1. VTDownMod
    2. VO
      singulars
      1. POBlock Matrix Transpose
      1. This table or related slice is empty.
      1. VTDownMod
    3. VO
      singulars
      1. POBlock Matrix Transpose
      1. This table or related slice is empty.
      1. VTUpMod
    1. COWhat do you mean by "the code is not working as expected". What is it doing? What were you expecting?
      singulars
      1. POBlock Matrix Transpose
      1. USMatthew Strawbridge
    2. COIt is displaying the first row of orignal matrix and gives segmentation fault
      singulars
      1. POBlock Matrix Transpose
      1. USJustin Carrey
    3. COI think your matrix is supposed to be encoded in a single array, not in an array of arrays. See the `Edit 2` of the linked question.
      singulars
      1. POBlock Matrix Transpose
      1. USdidierc
 

Querying!

 
Guidance
A row detail

Detail views are divided into sections. All the information in the data section comes from columns in the selected row. The other sections display data from other, related rows.

Related data can be related in a to-one or a to-many fashion. Captions of data related in a to-many fashion link to a list view showing a filtered view of the table.

Try moving around until you find a non-empty to-many entry and click on the label to get to one. You can move back to the root by clicking on the database name in the header.

SQuiL has stopped working due to an internal error.

If you are curious you may find further information in the browser console, which is accessible through the devtools (F12).

Reload