|Subject:||Re: [Help-glpk] Got a wrong order of column by lpx_get_mat_row(lp, j, ndx, val)?|
|Date:||Wed, 19 Jan 2005 11:05:17 -0500|
|User-agent:||Mozilla Thunderbird 0.9 (X11/20041124)|
Michael Hennebry wrote:
On Wed, 19 Jan 2005, [iso-2022-jp] $B%m!!%3%/%f%&(B wrote:Dose anyone meet this problem: for example in jth row : a*x-y+b*z=0; by len=lpx_get_mat_row(lp, j, ndx, val), I found val=[-1,a,b], that mean the order of column is y,x,z. I added two new columns to this row like: ndx[len+1]=w, ndx[len+2]=v, val[len+1]=d, val[len+2]=e, len+=2 lpx_set_mat_row(lp,j,len,ndx,val) then I thought the jth row should be a*x-y+b*z+d*w+e*v=0, but when I tried len=lpx_get_mat_row(lp, j, ndx, val) again, I found it's d*w+e*v+a*x-y+b*z=0. I wonder whether the order of columns in row is fixed and how the order of columns in a row is arranged there.My recollection is that there is nothing in the documentation that says lpx_get_mat_row will always return columns in the same order. Not even if you don't edit the problem.
I agree with Michael. This issue came up when testing the GLPK interface to COIN-OR/OSI. One of the tests for OSI fed in an instance and read some of the data back out. It initially failed for GLPK because it expected the data in a different order, even though what GLPK is doing is perfectly correct. In that case we had to modify the test itself.
-- Brady Hunsaker Assistant Professor Industrial Engineering University of Pittsburgh http://www.engr.pitt.edu/hunsaker/
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