|
I'm not sure how to remove redundant equations, but in case you need to use least squares to estimate a likely set of parameter values, you'll need to use statistical methods to estimate the precision. In a typical least squares solution, you would look at the variance-covariance matrix and use that to estimate the standard errors in the parameter estimates.
In typical least squares there are some empirical methods to do all of that, but I'm not aware of a general algorithm.
CQ de W5ALT
Walt Fair, Jr., P. E.
Comport Computing
Specializing in Technical Engineering Software
|
|
|
|
|
Walt Fair, Jr. wrote: The problem is how to ensure that some of the equations are not redundant.
Walt Fair, Jr. wrote: Actually, if there are fewer unknowns than equations
If such equations are not redundant then they are incompatible. 
If the Lord God Almighty had consulted me before embarking upon the Creation, I would have recommended something simpler.
-- Alfonso the Wise, 13th Century King of Castile.
This is going on my arrogant assumptions. You may have a superb reason why I'm completely wrong.
-- Iain Clarke
[My articles]
|
|
|
|
|
Well, if everything is perfect, then they would be incompatible.
If there are measurement errors or other uncertainties, then they may all be valid estimates. That's exactly the situation that least squares estimates are designed to handle.
CQ de W5ALT
Walt Fair, Jr., P. E.
Comport Computing
Specializing in Technical Engineering Software
|
|
|
|
|
In the least square estimate you find the set of parameters that best fits the experimental data into the given equation. You have not incompatible equations.
Generally speaking, if you have more independent equations than unknows then you cannot find a solution.
If the Lord God Almighty had consulted me before embarking upon the Creation, I would have recommended something simpler.
-- Alfonso the Wise, 13th Century King of Castile.
This is going on my arrogant assumptions. You may have a superb reason why I'm completely wrong.
-- Iain Clarke
[My articles]
|
|
|
|
|
And Walt is correct that there's a linear algebra method for doing least squares to find the "best" solution to the equations. If you have M equations and N unknowns, you have an MxN matrix times a Nx1 vector of unknowns giving a known Nx1 vector. You multiply both sides by the transpose of the matrix giving an (NxM) x (MxN) x (Nx1) = (Nx1) so you end up with an NxN matrix to do your solution with. If I remember right, the underlying principle is finding the best "projection".
Once you agree to clans, tribes, governments...you've opted for socialism. The rest is just details.
|
|
|
|
|
Simply put, you cannot solve:
x + y = 2
x - y = 0
x + 3y = 4
If the Lord God Almighty had consulted me before embarking upon the Creation, I would have recommended something simpler.
-- Alfonso the Wise, 13th Century King of Castile.
This is going on my arrogant assumptions. You may have a superb reason why I'm completely wrong.
-- Iain Clarke
[My articles]
|
|
|
|
|
CPallini wrote: Simply put, you cannot solve:
x + y = 2
x - y = 0
x + 3y = 4
You most certainly can find a solution. Whether it makes sense or not depends on what the equations represent. If, due to measurement or statistical errors, they really are representing the same set of parameters, then you can use least squares.
If all have the same importance and have been correctly normalized, etc., blah, blah, you simply find the minimum of:
[(x + y - 2)^2 + (x - y)^2 + (x + 3*y - 4)^2] w.r.t. x and y
If the minimum happens to be zero, the solution is exact. Otherwise it is an estimate of the parameters. The formal mathematical statement of the problem is something like
Find the set of x<small>i</small> that minimizes S = Sum{[f<small>j</small>(x<small>i</small>) - C<small>j</small>]^2}.
You can also add additional constraints to bound the problem and turn it into a nonlinear optimization problem.
CQ de W5ALT
Walt Fair, Jr., P. E.
Comport Computing
Specializing in Technical Engineering Software
|
|
|
|
|
Yes, you may indeed solve another problem, namely:
Given
f(x,y)=(x+y-2)^2 + (x-y)^2 + (x+3*y-4)^2
find the value of the pair {x,y} which minimize f(x,y).
However, that has not to do with the original linear algebric system.
The algebric system has not solutions according to the Rouché-Capelli theorem (and common sense).
Anyway, might be the OP really needed the solution to the least squares problem (i.e. I misunderstood his requirements), who knows?
If the Lord God Almighty had consulted me before embarking upon the Creation, I would have recommended something simpler.
-- Alfonso the Wise, 13th Century King of Castile.
This is going on my arrogant assumptions. You may have a superb reason why I'm completely wrong.
-- Iain Clarke
[My articles]
|
|
|
|
|
Yes, but you can solve
x + y = 2 + a
x - y = 0 + b
x + 3y = 4 + c
to find the x and y that makes a2+b2+c2 the minimum possible.
Clearly they will be not the "solution" of the system, but the value that minimize the "error" in having AX != B
Also note that - even in case of linear dependency - the method works well (it just gives the solution with a null minimum squared error, that is the -at that point- one and only solution).
Note also (not directly related to the post in answer) that saying that one particular equation is redundant is improper: all equation have the same dignity. Hence "find which equation to exclude" is a mis-posed problem. I can exclude another and get the same solution.
2 bugs found.
> recompile ...
65534 bugs found.
|
|
|
|
|
emilio_grv wrote: Yes, but you can solve
x + y = 2 + ax - y = 0 + bx + 3y = 4 + c
to find the x and y that makes a2+b2+c2 the minimum possible.
That is just another 'new' different problem.
And what would be the 'practical' usefulness of the solution of such new problem is questionable. Consider, for instance, if the original system is, by remote chance:
x = 1000
x = 0
emilio_grv wrote: Note also (not directly related to the post in answer) that saying that one particular equation is redundant is improper: all equation have the same dignity. Hence "find which equation to exclude" is a mis-posed problem. I can exclude another and get the same solution.
It was a quick way to say: "when you have two linearly dependent equations, you may esclude one of them to find the solution", of course all the equations have the same dignity in the system, anyway you can arbitrarly choose one to solve the system.
If the Lord God Almighty had consulted me before embarking upon the Creation, I would have recommended something simpler.
-- Alfonso the Wise, 13th Century King of Castile.
This is going on my arrogant assumptions. You may have a superb reason why I'm completely wrong.
-- Iain Clarke
[My articles]
modified on Saturday, July 10, 2010 11:21 AM
|
|
|
|
|
I've been trying to put some code together for setting a desired file creation date/time.
I also got introduced to the FILETIME structure (2 DWORD).
DWORD unsigned long 4,294,967,296 (possibles, including zero)
Hopefully I can get a string to be processed and set the file creation date/time.
So these would be the variables for the DWORD:
1 second 100
1 minute 6,000
1 hour 360,000
24 hours 8,640,000
1 year 3,153,600,000
Current resources on MSDN use SystemTime functions, out of fear of guiding someone to fake copyrighted material.
HANDLE File = CreateFile(L"My File.txt", GENERIC_WRITE, FILE_SHARE_WRITE, NULL, OPEN_ALWAYS, FILE_WRITE_ATTRIBUTES, NULL);
SetFileTime( File, &CreationTime, NULL, NULL);
CloseHandle(File);
|
|
|
|
|
What's your point?
If the Lord God Almighty had consulted me before embarking upon the Creation, I would have recommended something simpler.
-- Alfonso the Wise, 13th Century King of Castile.
This is going on my arrogant assumptions. You may have a superb reason why I'm completely wrong.
-- Iain Clarke
[My articles]
|
|
|
|
|
i want to set the file creation date to a specific time
|
|
|
|
|
This is what you want to do. Now, what is the question or problem?
If the Lord God Almighty had consulted me before embarking upon the Creation, I would have recommended something simpler.
-- Alfonso the Wise, 13th Century King of Castile.
This is going on my arrogant assumptions. You may have a superb reason why I'm completely wrong.
-- Iain Clarke
[My articles]
|
|
|
|
|
what's the question ?
Watched code never compiles.
|
|
|
|
|
i want to set the file creation date/time to a desired date/time
|
|
|
|
|
And what problem are you having in doing so?
"One man's wage rise is another man's price increase." - Harold Wilson
"Fireproof doesn't mean the fire will never come. It means when the fire comes that you will be able to withstand it." - Michael Simmons
"Man who follows car will be exhausted." - Confucius
|
|
|
|
|
Fareed Rizkalla wrote: Current resources on MSDN use SystemTime functions, out of fear of guiding someone to fake copyrighted material.
W.T.F. ?!
I which paranoia you've got lost ?
2 bugs found.
> recompile ...
65534 bugs found.
|
|
|
|
|
Is it possible to set C as the default to convert and compile in rather than c++?
If that is not possible, how do I set a specific project to C rather than C++?
(Trying to get a vb6 converted to native c rather than c++ without total rewrite.)
Thank You,
Don
|
|
|
|
|
Why don't you give the c (instead of cpp) extension to your files?
If the Lord God Almighty had consulted me before embarking upon the Creation, I would have recommended something simpler.
-- Alfonso the Wise, 13th Century King of Castile.
This is going on my arrogant assumptions. You may have a superb reason why I'm completely wrong.
-- Iain Clarke
[My articles]
|
|
|
|
|
The compiler driver works out what type of source file it's got based on the extension you give it. Call it .cpp and it'll use the C++ compiler, .c and it'll use the C compiler. You can overide this on a per source file basis by using /TC (compile as C) and /TP (compile as C++). It's an advanced option in the properties of the project.
Cheers,
Ash
|
|
|
|
|
Edit : Issue was mostly with the spawned EXE that did not handled parameters properly.
Now everything is working ok.
Thanks.
I'm trying to figure out a couple of issues I have with some path that contains spaces when using ShellExecuteEx :
The current directory contains space : C:\Users\me\Documents\Visual Studio 2008\Projects\asdcasd\asdcasd
TCHAR Buffer[MAX_PATH];
DWORD dwRet;
dwRet = GetCurrentDirectory(MAX_PATH, Buffer);
CString sWorkingPath;
sWorkingPath.Format( _T("\"%s\""), Buffer );
CString command ( _T("XMLtoPDF.exe"));
CString parameters( _T(""));
CString sExe;
sExe.Format ( _T("\"%s\\%s\""), Buffer, command);
SHELLEXECUTEINFO ShExecInfo = {0};
ShExecInfo.cbSize = sizeof(SHELLEXECUTEINFO);
ShExecInfo.fMask = SEE_MASK_NOCLOSEPROCESS;
ShExecInfo.hwnd = NULL;
ShExecInfo.lpVerb = _T("open");
ShExecInfo.lpFile = sExe;
ShExecInfo.lpParameters = parameters;
ShExecInfo.lpDirectory = sWorkingPath;
ShExecInfo.nShow = SW_SHOW;
ShExecInfo.hInstApp = NULL;
ShellExecuteEx(&ShExecInfo);
WaitForSingleObject(ShExecInfo.hProcess,INFINITE);
The exe spawns a console (it's a perl byte-compiled stand-alone) and tells me the path is not good : C:\Users\me\Documents\Visual does not exists.
I've checked the path and they all semms to be double-quoted to handle the spaces.
Am i missing something ?
Thanks a bunch.
Watched code never compiles.
modified on Thursday, July 8, 2010 3:52 PM
|
|
|
|
|
Suggestions:
1) Use GetShortPathName().
2) Use UrlEscape().
I'm not sure if either will work, however.
"One man's wage rise is another man's price increase." - Harold Wilson
"Fireproof doesn't mean the fire will never come. It means when the fire comes that you will be able to withstand it." - Michael Simmons
"Man who follows car will be exhausted." - Confucius
|
|
|
|
|
I have a CFormView class that hosts a Microsoft WebBrowser ActiveX control. I use the control to browse to various HTML pages. Some of these pages create pop-up pages, through some JavaScript buttons.
Now when I browse to the site through IE, and the pop-up windows are created, they work fine and display their contents. When I browse to the site through my app, the pop-up windows are created, but I get a script error saying "A security error has occurred". I can then continue by clicking on the "Yes" button, but nothing further happens.
In my application I browse to the pages through Navigate2("http://username:password@site.blah"), thus passing some security credentials to the page. Could this be the problem ? How do I pass these credentials on to the popup (of which I have no control) ? Any other ideas as to what the problem could be ?
Thanks !
OD
|
|
|
|
|
On accessing a class member variable, the process crashes.
The class variable is a structure instance of size 108 bytes which is properly padded.
On Get_proc() which returns the structure pointer(address of the instance) it crashes.
The Get_proc() is called from another class scope.
The Stack points within the Get_proc() call and then accessing the structure address it crashes. The structure pointer is not NULL.
On making the structure instance scope as global, it does not crash.
Please do give your inputs.
user_m is a properly padded aligned structure with variables BYTE and WORD.
class User
{
private:
user_m inst_user_m;
public:
user_m* Get_proc();
}
user_m* Get_proc()
{
if (&user_m)
return &user_m;
}
|
|
|
|
|
General 
News 
Suggestion 
Question 
Bug 
Answer 
Joke 
Praise 
Rant 
Admin 
Submit an article or tip
