MATLAB: Set working path at startup

Many times when MATLAB is started there is a certain program that you want to work on. In order to work on this program, the current directory or path of that program must be changed or set.  This little script here will prompt the user for the module to work on and then add that directory to the path listing. When MATLAB is terminated, that path will not be saved.

% startup.m

% Set Production Directory
prod='~/MATLAB/Production/';

% Prompt user for module name
module=input('What module do you want to work on? ','s');

% If module is set, add to top of path. Otherwise don't add
if ~isempty(module)
 path([prod,module],path);
end

Place the startup.m in your MATLAB work directory.

Plotting in MATLAB / Making Plots Look Pretty

Alright, well, here's the scoop. Ditto wanted a v2.0 remake of a post that we started late last year. And, well, I give him whatever he wants. So, without further ado, here's Pretty Plots in Matlab, v2.0.

Using MATLAB to crank through some calculations, but having trouble making the plots pretty? Here's an example that should make a nice looking plot that's ready to be inserted into a report.

X=[1 2 3 4 5 6 7 8 9 10];
Y=X.^2;

xmin=0;
xmax=11;
ymin=0;
ymax=110;

figure
set(gca,'fontsize',14)
set(gcf, 'PaperSize', [8. 6.],'PaperPositionMode', 'auto');
plot(X,Y,'k^','markersize',10,'markerfacecolor','r')
legend('mylegend','location','northeast');
xlabel('my $x$ label','Interpreter','latex','fontsize',16);
ylabel('my $y$ label','Interpreter','latex','fontsize',16)
AXIS([xmin xmax ymin ymax])
print('-r600','-dpdf',['filename','.pdf'])

Copy, paste, and run, and you should get this (in the directory your current directory):



Alright, a quick rundown.

1. The 'figure' command is letting MATLAB know that we're making a picture with all the following attributes.
2. The 'set gca' command is setting the axes, which have the default handle 'gca', to have a font size of 14 here. This will control the size of the numbering on the axes, as well as the size of the font in the legend.
3. The 'set gcf' command is setting the paper size to 8" by 6", a size I find works well with the default figure output of MATLAB. This will prevent you from having to crop the plot later in a third-party photo editor.
4. The 'plot' command lists the X and Y arrays youd like to plot, 'k^' plots black upward facing triangles in a 'marker size' of 10pt, and filled red.
The 'legend' command puts in your legend, one entry per pair of vectors being plotted, in the northwest position.
5. The 'xlabel' and 'ylabel' commands are pretty straightforward, but the interpretter command displays the labels in the default LaTeX font instead of the MATLAB font. You can use the '$$' pairing to put in maths (the x and y).
6. The 'axis' command sets the range for x and y, just comment this out if you like what MATLAB does.
7. The 'print' command will save your figure as .pdf with the filename you specify in the current directory (where your .m file is). Here, you can always specficy a path if you'd like to save figures in a different folder.

Still to come, using str2num and num2str to automatically number plots that are part of a for loop, or to name output graphs based on input data.

Pretty Plots in MATLAB

Using MATLAB to crank through some calculations, but having trouble making the plots pretty? Here's an example that should make a nice looking plot that's ready to be inserted into a report.

figure
set(gca,'fontsize',14)
set(gcf, 'PaperSize', [8. 6.],'PaperPositionMode', 'auto');
plot(X,Y,'k^','markersize',10,'markerfacecolor','auto')
legend('mylegend','location','northeast');
xlabel('myxlabel','Interpreter','latex','fontsize',16);
ylabel('myylabel','Interpreter','latex','fontsize',16)
AXIS([xmin xmax ymin ymax])
print('-r600','-dpdf',['filename','.pdf'])

Alright, a quick rundown.

1. The 'figure' command is letting MATLAB know that we're making a picture with all the following attributes.
2. The 'set gca' command is setting the axes, which have the default handle 'gca', to have a font size of 14 here. This will control the size of the numbering on the axes, as well as the size of the font in the legend.
3. The 'set gcf' command is setting the paper size to 8" by 6", a size I find works well with the default figure output of MATLAB. This will prevent you from having to crop the plot later in a third-party photo editor.
4. The 'plot' command lists the X and Y arrays youd like to plot, 'k^' plots black upward facing triangles in a 'marker size' of 10pt, and automatically filled.
The 'legend' command puts in your legend, one entry per pair of vectors being plotted, in the northwest position.
5. The 'xlabel' and 'ylabel' commands are pretty straightforward, but the interpretter command displays the labels in the default LaTeX font instead of the MATLAB font. You can use the '$$' pairing to put in maths.
6. The 'axis' command sets the range for x and y, just comment this out if you like what MATLAB does.
7. The 'print' command will save your figure as .pdf with the filename you specify in the current directory (where your .m file is). Here, you can always specficy a path if you'd like to save figures in a different folder.

Still to come, using str2num and num2str to automatically number plots that are part of a for loop, or to name output graphs based on input data.

MATLAB: Don't ', transpose(it)

Doing a little homework for ME 7040, I discovered that there is more to transposing a matrix than just rows becoming columns and vice versa. I was doing a simple stress, strain, displacement analysis of a beam under static load. The code snippet in question is when the elemental stiffness matrix needed to be calculated by:

k = int(int(B'*D*B,r,-0.5,0.5),s,-0.5,0.5)

B is a 3xn matrix of shape functions and D a 3x3 relationship of Modulus of Elasticity and Poisson's ratio. There is obviously more to this code, including the calculations of stress and strain and the writing of an output file.

Running the code using the prime ('), the code took 143.106 seconds to run. I was initally confused by how long it took because the matrices were not that large. I then heard about the function transpose() and decided to use that. In code form:

k = int(int(transpose(B)*D*B,r,-0.5,0.5),s,-0.5,0.5)

This took only 19.735 seconds to run. So digging a little further, the operator ', also checks for complex conjugates of the matrix as well.

In conclusion, if you know that you are not dealing with complex numbers, you may want to use the transpose function and not its operator.

Tip: To time the running time of your code, put tic on the top line and toc on the last line.