fprintf into a stored variable

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WhatIsMatlab-
WhatIsMatlab- 2016-2-12
评论： per isakson 2016-2-15
Instead of using fprintf I want to store all the i, xe, and f(xe) into a vector instead. That way I can call them later. Also I had another problem where I wanted to use another 'i' later on in the code. But it only allowed me to use 1. How can you use two different 'i's. So they don't get mixed up.
f = @(x) x^2-6;
xl = 0;
xu = 10;
xe = (xu+xl)/(2);
acc = 0.00001;
while abs(f(xe))> acc
i = i + 1;
fprintf('%d)\t%f\tf(x)=%f\n',i,xe,f(xe));
if (f(xe)*f(xl)) < 0
xu = xe;
else
xl = xe;
end
xe = (xu+xl)/2;
end

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per isakson
per isakson 2016-2-13
编辑：per isakson 2016-2-13
Add
M = zeros( 0, 2 );
before the loop and replace
fprintf('%d)\t%f\tf(x)=%f\n',i,xe,f(xe));
by
M( end+1, 1:2 ) = [ xe, f(xe) ];
You'll get a warning about "Growing ..." , but if speed is acceptable ignore it.
&nbsp
"fprintf into a stored variable" &nbsp If understood literally, replace
fprintf('%d)\t%f\tf(x)=%f\n',i,xe,f(xe));
by
C{end+1,1} = sprintf('%d)\t%f\tf(x)=%f\n',i,xe,f(xe));
and add C=cell(0,1) before the loop
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per isakson
per isakson 2016-2-15
  • "but I got an error" &nbsp we cannot help if you don't show what you did and what error Matlab reported.
  • "a better way of achieving this" &nbsp length(s) and length(m) tell the number of iterations in the two loops.
per isakson
per isakson 2016-2-15
This example illustrates
  • two ways to count the number of loop iterations
  • two ways to store result in the loop
N = 1e6;
M1 = zeros( 0 );
ii = 0;
M2 = nan( N, 1 ); % Pre-allocate
while sqrt(ii) < sqrt(N) - 10
ii = ii + 1;
M1( end+1, 1 ) = ii;
M2(ii) = ii;
end
M2(isnan(M2)) = [];
disp( all( M2 == M1 ) )
disp( ii )
disp( length(M1) )
disp( length(M2) )
outputs
1
980100
980100
980100
where "1" shows that M1 and M2 are identical.
[Run and Time], i.e. the profiler, shows that "M1" is slower.

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