Why does MATLAB 6.5 (R13) give an Assertion Failure when I try to index into a matrix with zero from my MATLAB function?

Question

MathWorks Support Team 2009-6-27

0
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此问题的直接链接

https://ww2.mathworks.cn/matlabcentral/answers/102424-why-does-matlab-6-5-r13-give-an-assertion-failure-when-i-try-to-index-into-a-matrix-with-zero-from

I have the following code:

function test
alpha = 0.1;
N = 10;
wtarget = rand(200,1);
w = zeros(200,1);
lastval = 0;
for i=1:100
% make random a vector with N ones
a = zeros(200,1);
for c=1:N
a(fix(rand*200)) = 1;
end
error = a'*wtarget - a'*w;
w = w + alpha/N*a*error;
val = (wtarget-w)'*(wtarget-w)
disp( val-lastval )
lastval = val;
end

If I run this code in MATLAB, I get the following crash:

 -----------
 Assertion detected at Wed Dec 18 17:20:39 2002
 -----------
 Assertion failed: hdr->in_use != 0, at line 1218 of file ".\mwmem.c".
 Attempt to free previously freed memory
 Configuration:
 MATLAB Version: 6.5.0.180913a (R13)
 Operating System: Microsoft Windows 2000
 Window System:Version 5.0 (Build 2195: Service Pack 2)
 Processor ID: x86 Family 6 Model 8 Stepping 6, GenuineIntel
 Virtual Machine:Java 1.3.1_01 with Sun Microsystems Inc. Java HotSpot(TM) Client VM
 (mixed mode)
 Stack Trace:
 [0] matlab.exe:_mnSignalHandler(0xffffffff, 0, 0, 1) + 592 bytes
 [1] matlab.exe:void __cdecl ThrowAssertion(void)(0, 0x7a748ba0, 0x65737341, 0x6f697472) + 162 bytes
 [2] matlab.exe:void __cdecl MATLABAssertFcn(char const *,char const *,int,char const *)(0x7a741868 ": hdr->in_use != 0,", 0x7a74100c ".\mwmem.c", 1218, 0x7a741938 "Attempt to free previously freed..") + 131 bytes
 [3] libut.dll:_ut_assertstr(0x7a741868 ": hdr->in_use != 0,", 0x7a74100c ".\mwmem.c", 1218, 0x7a741938 "Attempt to free previously freed..") + 25 bytes
 [4] libut.dll:_mw_free(0x18d93010, 2, 0x18f0e4f8, 0x00dfc8bc) + 542 bytes
 [5] libut.dll:_utFree(0x18d93010, 0x18f0e4f8, 0x18f0e4f8, 0x00dfc8d8) + 25 bytes
 [6] libmx.dll:_mxDestroyArrayContents(0x18f0e4f8, 0x18f0e4f8, 0xfffffff7, 0x18f0e4f8) + 209 bytes
 [snip]

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Answer 1

MathWorks Support Team 2009-6-27

0
链接

此回答的直接链接

https://ww2.mathworks.cn/matlabcentral/answers/102424-why-does-matlab-6-5-r13-give-an-assertion-failure-when-i-try-to-index-into-a-matrix-with-zero-from#answer_111770

This bug has been fixed for Release 14 (R14). For previous releases, please read below for any possible workarounds:

This is a bug in MATLAB 6.5 (R13) that has been reported to our development staff for further investigation. This bug is caused by the MATLAB Accelerator.

To work around the problem, you can turn off the MATLAB Accelerator with the following command:

feature jit off

MATLAB will then error out instead of giving an Assertion Failure. This will make it more obvious as to where the erroneous code lies.