I often have function such as:
sin(a*w*t + p)
where:
w = natural frequency
t = time
a,p = parameters (which I can vary)
As you can see if you want to vary a,p, you can do so via the standard interface but it's not very convenient. So I thought I'd look for a GUI which has a slider for each parameter. Does such a thing exist?
I've never seen one so I thought I'd quickly write one. However, I'm worried that due to lack of time and knowledge of matlab I will cause problems such as generating too many plot commands when the slider is moved instead of just one. Of course I also have the problem that I want to specify a field where the user can specify the function e.g. by typing sin(a*w*t +p) in a text field and then specify what each variable means which I currently don't know how to do (it looks like a parsing task). Can I do this or should I go with a predefined set of functions?
You can find similar projects in Matlab File Exchange as example.
For instance:
Integral Tool
Function Parameter Slider
I didn't have a look at the code but according to the screenshots, it should help you.
Regarding the function input feature, you can use the function eval (with a few checks on the input if you need reliability). If you want to allow any parametric variable, it may be harder.
Related
I want to integrate a Modelica variable over time, just for convenience in plotting and post-processing. The variable I want to integrate over time is the power of a compressor so that I get the total energy. The first idea would be to add these lines:
Modelica.Units.SI.Power P_comp;
Modelica.Units.SI.Energy E_comp;
equation
P_comp = der(E_comp);
Is that the recommended way, or are there (better?) alternatives? Is it expected to influence the selection of dynamic states?
Assuming that those two lines are the only ones using E_comp that should work.
Basically E_comp will be part of its own separate state-selection block and changes there shouldn't influence anything else.
However, state selection consists of a number of algorithms and heuristics so it is difficult to formally guarantee that any change does not influence it.
I could imagine some strange possibilities that would break this, but I don't think anyone has implemented them - and I don't see a use-case for them (except to mess up cases like this).
And if you instead of integrating want to differentiate a signal it is a lot messier.
I thought this should be a simple task, I just can't find the way to do it:
I am using 'imregister' (MATLAB) to register two medical X-ray images.
To ensure I get the best registration outcome as possible, I use some image processing techniques such as contrast enhancement, blackening of objects that are different between images and even cropping.
The outcome of this seems to be quite satisfying.
Now, I want to perform the exact same registaration on the original images, so that I can display the two ORIGINAL images automatically in alignment.
I think that an output parameter such as tform serves this purpose of performing a certain registration on any two images, but unfortunately 'imregister' does not provide such a parameter, as far as I know.
It does provide as an output the spatial referencing object R_reg which might be the answer, but I still haven't figured out how to use it to re-preform the registration.
I should mention that since I am dealing with medical X-ray images on which non of the feature-detecting algorithms seem to work well enough to perform registration, I can only use intensity-based (as opposed to feature-based) registration, and therefore am using 'imregister'.
Does anyone know how I can accomplish this?
Thanks!
Noga
So to make an answer out of my comment, there are 2 things you can do depending on the Matlab release you are using:
Option 1: R2013a and earlier
I suggest modifying the built-in imregister function by forcing tform to be an output and save that function under another name.
For example:
function [movingReg,Rreg,tform] = imregister2(varargin)
save that, add it to your path and you're good to go. If you type edit imregister you will notice that the 1st line calls imregtform to get the geometric transformation required, while the last line calls imwarp, to apply that geometric transformation. Which leads us to Option 2.
Option 2: R2013b and later
Well in that case you can directly use imregtform to get the tform object and then use imwarpto apply it. Easy isn't it?
Hope that makes things clearer!
My initial problem is that I have a continuous transfer function which coefficients change with time.
Currently the TF's coefficients are expressed in function of the block mask parameters. These parameters are tunable, and if I change the value in the mask parameters dialog during a simulation the response seems to react appropriately.
However how can I do just that in the code/block flow? Basically, I
have the block parameter 'maskParam' which is set using the mask
parameters dialog, and in the mask initialization commands:
'param=maskParam'. 'param' is used in the transfer function and I
would like to change it in real time (as param=maskParam*f(t)).
I have already looked around and found relevant solutions but either it's unbelievably complicated; or the only transfer function which we are allowed to modify at runtime is discrete and 1) I would like to avoid z-transforming my quite complex TF (I don't have the control toolbox) 2) The sampling time seems to be fixed.. None uses this "dirty" technique of updating parameters, maybe that's the way around?
To illustrate:
I am assuming that you want to change your sim parameters whilst the simulation is running?
A solution is that you run your simulation for inf period and use/change a workspace variable during the simulation period to make the changes take effect.
for Example:
If you look at the w block, you can set it's value in runtime, by doing this:
set_param('my_model_name/w', 'value', 100); % Will change to 100 immediately
You can do similar things with arrays (i.e. a list of coefficients in your case).
HINT FOR YOU
You are using discrete transfer function block. Try the following:
1) Give your block a name e.g. fcn_1
2) In your script, type set_param('your_model_name/fcn_1', 'numerator', '[1 2]'); This will set the numerator value to [1 2]. Do the same for denominator.
3) You should be able to understand, through this exercise, how to handle the property names etc. so that you can change/get them using set_param/get_param.
I leave you to investigate further.
The short answer is that Simulink blocks are not really designed to do this. By definition, a transfer function is Liner-Time Invariant, meaning its characteristics (read coefficients) do not vary with time.
Having said that, there are some workarounds, such as the ones you mentioned in your question. These are the correct way to approach the problem I'm afraid, other than the set_param method suggested by #ha9u63ar. See also this blog on the subject on the MathWorks web site.
I am trying to find more information on making a custom PID block in MATLAB. I have most of it done but there are a few parameters that I don't really understand and as such I don't know what value to give them. NOTE I am NOT asking for help tuning PID gains.
They are all inside the filter coefficient block:
When I open the block I have to set a few parameters (output min/max, data type, parameter min/max, etc.). Can someone explain to me what these mean? I can't find good resources anywhere. The only thing that I've tried which works is setting each to [] (i.e. -inf) and the input/output data types to 'Inherit: Inherit via internal rule' but then my output goes to hell. If I copy paste the blocks from the PID block there are a bunch of variables which I haven't defined anywhere so the program won't even compile.
Can someone point out some good resources for this or else explain it? Thanks!
You should get your blocks from the standard Simulink library, not from under the PID block mask. The ones under the mask have been set-up to use variables that are passed from/through the mask, which you are not doing.
The block you have circled is just a gain block (from the Math library).
You most likely won't need to make any changes to the default settings of the block other than the constant value (which needs to be the N that you want to use in the approximation of the derivative term in your controller).
To answer your specific question about what the parameters are, some of them are used to specify data types (if you don't want to use the default double precision), some are only used in code generation, some others only for other specific tasks.
All of them are described (in more, or sometimes less, detail) in the doc for the block, obtained by pressing the help button on the block's dialog.
I have some programs written in Matlab that I need to run several times for some reasons (debugging, testing with different input, etc...)
But, there are a lot's of graphs that are plotted by the programs and its various functions such that everytime I run the program, I have to wait for all the graphs to be displayed, which is very annoying and time consuming (especially when you are working with a small laptop).
After the program is executed, I close them with a close all.
So my question is:
Is there a way to disable all plots/figures/graphs in Matlab? either in the options, or by executing a certain code like disable plot and enable plot to ensure that no figures are being displayed.
I know that I can just browse the code and comment the plotting part, but I don't want to forget to uncomment.
Try some combination of the two commands:
set(gcf,'Visible','off') % turns current figure "off"
set(0,'DefaultFigureVisible','off'); % all subsequent figures "off"
The second one, if you put it near the beginning of your program, might do the trick for you. Of course, it is still creating the plots, which might be undesirable for computation time and/or RAM issues.
This is a classic reason to avoid Matlab when one can. It fosters bad programming design. To solve this problem correctly, you should create something that lets you "flip a switch" at the highest level of your program and control whether plots show or do not show. Perhaps it even has gradations of the show/don't show option so you can select different types of plots that do/do not show depending on what diagnostics you are running.
Ideally, you'd want this "flip a switch" creation to be a class that has access to visibility and plot functions of other objects. But because interactive object-orientation is so cumbersome in Matlab, it's often not worth the effort to develop such a solution, and most people don't think about this design aspect from the outset of their project.
Matlab would encourage someone to solve this by making flag variables like "isPlotVisible" or something, and creating functions that always accept such flags. I agree this is a bad design.
You could run matlab from the command line with:
matlab -nojvm
but then you don't get the GUI at all. Alternatively, you could write a file 'plot.m':
function h = plot(varargin)
h = [];
end
which doesn't do anything. If this is in the working directory (or somewhere else near the top of the path), then plot will call your function instead of the 'real' plot. You'd need to do the same from any other graphing functions you call.
The closest way I know of 'turning off plotting' would be a folder of such functions that you can add to the path to disable plotting, and remove to enable.
The previous methods are fine, but an easy and good habit to take is to use a "on/off parameter". So basically, at the beginning of your code, you can add something like:
DisplayFigure = 1; %1 = display, 0 = no display
After that, add "if DisplayFigure == 1 ... end" for all your plotting related commands, where the commands should be inside the if statement (the ... above). Hence you won't even compute the plots, which will save you a lot of time and memory. You just have to change the value of the variable "DisplayFigure" to plot or not the figures.