Loop until Matrix value exceeds value

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Buster
Buster 2021-9-13
回答： dpb 2021-9-13
I have a script for truss analysis. The calculation is set up Ax=b. A is the govenring equations from the truss anaylsis while x is m. Thus b is the stresses in the members depending on m. m ranges from values 1-7. i need to make a loop that ends the calulations after a certain value of matrix b is met and then displays the previus iteration as "max allowable mass". my issue is designating that "a value inside b" > given value. and having the loop re-run for the acceptable tolerances.
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Buster
Buster 2021-9-13
Essentially i only have A=9x1 and x=1:7. B is the resulting values of A*x and they are given as 9 different values which is what i need. Basically i need a loop to run through the caluclation of A*x=B until a single value of the 9 given by B is over 60. once any of said values hits 60 i need the loop to stop and display all 9 B values that are accepted and the x value that gives these B values that are less than the tolerance of 60. does this help?
Jan
Jan 2021-9-13
If A ia [9 x 1] vector and x is [1 x 7], A * x is a [9 x 7]. How can this be given as 9 different values? Over which calculation do you want to run a loop?

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dpb
dpb 2021-9-13
% pseudo code, salt to suit...
A=[...]; % initialize A here
maxB=60; % the test value
for x=1:7
B=A*x; % compute B
if all(B)<=maxB % everything AOK so far...
fprintf(['X=%d, B[]=' repmat(numel(B),'%f.2 ') newline],X,B);
end
end
The above prints every time the condition is met rather than waiting unitl it fails and then backing up one level -- that's doable, takes a little more logic to save the previous values as well so I took the easy way out here.
The key MATLAB point here is the use of any and/or all to make the logic test -- read the documentation for them to see why.
I don't know the problem your'e trying to solve, of course, but it seems to me that rather than use the multiples of 1:N it would make more sense to solve the system to find the critical mass value instead.

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