Chapter3.1-2

# Chapter3.1-2 - Script files In the process of zooming on...

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Unformatted text preview: 1/12/09 Script files. In the process of zooming on the solution we have repeatedly used certain lines. We might as well put them into a file using the Matlab editor. So I save the following lines y=cos(x) plot(x,y) grid xlabel('x') ylabel('cos(x)') In a file I call cosroot. Then I use it >> x=0:0.1:2; >> cosroot y = Columns 1 through 10 1.0000 0.9950 0.9801 0.9553 0.9211 0.8776 0.8253 0.7648 0.6967 0.6216 Columns 11 through 20 0.5403 0.4536 0.3624 0.2675 0.1700 0.0707 0.0292 0.1288 0.2272 0.3233 Column 21 0.4161 1 0.5 cos(x) 0 -0.5 0 0.2 0.4 0.6 0.8 1 x 1.2 1.4 1.6 1.8 2 And zoom >> x=linspace(1.4,1.6,10); cosroot y = 0.1700 0.1480 0.1260 0.1039 0.0818 0.0596 0.0375 0.0152 0.0070 0.0292 0.2 0.15 0.1 cos(x) 0.05 0 -0.05 1.35 1.4 1.45 x 1.5 1.55 1.6 >> It is also possible to make this a function, so that we can include the linspace in the file. function y=cosinter(xl,xu,n) %generates x values in the interval(xl,xu) and plots the cosine function i %the interval x=linspace(xl,xu,n); y=cos(x) plot(x,y) grid xlabel('x') ylabel('cos(x)') Then we invoke the function >> y=cosinter(1.5,1.6,10); y = 0.0707 0.0596 0.0486 0.0375 0.0263 0.0152 0.0041 0.0070 0.0181 0.0292 0.08 0.06 0.04 cos(x) 0.02 0 -0.02 -0.04 1.5 1.52 1.54 1.56 x 1.58 1.6 1.62 1.64 We can also have the function prompt us for the data, using the input command. Now the Mfile will be function y=cosprompt %generates x values in the interval(xl,xu) and plots the cosine function i %the interval xl=input('xlower') xu=input('xupper') n=input('number of intervals') x=linspace(xl,xu,n); y=cos(x) plot(x,y) grid xlabel('x') ylabel('cos(x)') And the output is: >> cosprompt xlower 1.5 xl = 1.5000 xupper 1.6 xu = 1.6000 number of intervals 11 n = 11 y = Columns 1 through 10 0.0707 0.0608 0.0508 0.0408 0.0308 0.0208 0.0108 0.0008 0.0092 0.0192 Column 11 0.0292 ans = Columns 1 through 10 0.0707 0.0608 0.0508 0.0408 0.0308 0.0208 0.0108 0.0008 0.0092 0.0192 Column 11 0.0292 0.08 0.06 0.04 cos(x) 0.02 0 -0.02 -0.04 1.5 1.52 1.54 1.56 x 1.58 1.6 1.62 1.64 To display information, we have the disp command. Consider calculating the eigenvalues of a matrix. Generate first a simple matrix sig=ones(3,3) sig = 1 1 1 1 1 1 1 1 1 >> disp('eigenvalues') eigenvalues >> disp(eig(sig)) 0.0000 0 3.0000 Notice that even though two of the eigenvalues are exactly zero, for the first one, computation errors apparently give a small negative value. format short e >> disp(eig(sig)) 3.3307e016 0 3.0000e+000 Instead of changing the display format every time we want to check something like that, we can also specify the format by using an fprintf command instead of a display command. >> fprintf('eigenvalues \n, %e %e %e', principal) eigenvalues , 3.330669e016 0.000000e+000 3.000000e+000>> Assuming that the matrix is a stress matrix, we can create an Mfile to calculate the maximum shear function maxshear(stress_tensor) %generates the maximum shear stress for a given stress tensor principal=eig(stress_tensor); maxshear=(max(principal)min(principal))/2; fprintf('maximum shear= %e', maxshear); Then we invoke it as >> maxshear(sig) maximum shear= 1.500000e+000>> ...
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