This is my code:
%Activity 3.4 An object is thrown vertically with a speed vo reaches at
%height h at a time t.
function t = time(h,vo,g)
t = roots([0.5*g,-vo,h])
%Testing the function
test = time(100,50,9.81)
I've looked through different solutions but still can't figure out why I keep getting this error.
The error is happening on the line t = roots([0.5*g,-vo,h]).
Three comments:
You are probably pushing the Play button in the MATLAB editor. Don't do that. Forget that it even exists. Define h, vo and g in your Command Prompt, then do t = time(h, vo, g); in the Command Prompt. Again, do not push the Play button.
Make sure your working directory is set to where you defined the function time. MATLAB can't find this function that you defined. If you don't know how to do that, check out this from MathWorks: http://www.mathworks.com/help/matlab/ref/cd.html
Your error says it's trying to use a file called A3_4, yet your function is called time. In other words, It looks like you called your file A3_4.m yet it needs to be called time.m. Make sure it's in a file called time.m, then try again. That's one of MATLAB's cardinal rules. When you define a function, the function name and file name need to match.
Do all of those three steps in order, and you will be laughing and singing like these guys below:
(source: kym-cdn.com)
Related
I am trying to amend the example given here for creating a dynamic masked subsystem, where I want to dynamically change the number of imports and outports to an S-Function.
I have a very simple S-Function implemented in C (it's the timestwo example in the documentation) and for which I wish the user to be able to define the number of inputs and number of outputs in a mask. The intention is then, within the S Function, to manipulate the received input values and write to the output values. The S-Function will eventually do some quite complicated stuff and I need multiple instances of it in Simulink, hence why I want it defined in a library.
I have put the S-Function into a library and unlocked it by choosing Diagram->Unlock Library.
I have defined 2 variables, numInports and numOutports in the Parameters & Dialog pane of the mask editing window.
I then add the following to the Initialization pane:
blocks = find_system(gcb,...
'LookUnderMasks','on',...
'FollowLinks','on',...
'RegExp', 'on',...
'BlockType', 'port');
if ~isempty(blocks)
Simulink.SubSystem.deleteContents(gcb);
end
for n=0:(numInports - 1)
label = sprintf('/In%d', n);
add_block('built-in/Inport',[gcb,label]);
end
for n=0:(numOutports - 1)
label = sprintf('/Out%d', n);
add_block('built-in/Outport',[gcb,label]);
end
The intention is for the initialisation to delete all imports and outports when the parameters are changed, then recreate them. I then save the model within the library.
The find_system() command should find and delete all blocks with port in the type, as suggested here and here.
I have created a model that uses this library model S Function implementation. However, when I update the parameters, I get the error:
Error in 'MyModel/MyLibrarySFunction': Initialization commands cannot be evaluated. Caused by:
A new block named 'MyModel/MyLibrarySFunction/In0' cannot be added.
Can anybody please advise what is going wrong here?
EDIT:
The documentation for find_system() has all as a valid parameter value, not the on I used and which was in the documentation example, but this seems to have no effect when I change it. I added:
msg = sprintf('Num blocks: %d', numel(blocks));
disp(msg);
just after the find_system() call and get 0 for the number of blocks found, so I guess the problem may be that In0 is not deleted and hence I am trying to reinsert it.
I have a problem that I'm having a hard time even framing for this question's title.
I have a library that calculates the properties of refrigerants. For example, you give pressure and enthalpy, and it tells you the temperature. That library is coded in Fortran with a mex file to interface with Matlab. Now, I am 100% sure that library is thoroughly debugged (it was coded by people much smarter than me, and has been used for almost a decade). The problem is definitely in how I call it.
And that problem is this. I call the library from a StartFcn callback (a .m script file) in a subsystem of a simulink model. The first time I run this model, it runs perfectly. The values I'm sedning to the function are therefore correct. The second time I run it, however, it crashes. The inputs both times are exactly the same.
Also, if I do a clear all between the two runs, then there is no crash. But if I do only clearvars or clear, I still get a crash. When I debug and look at the variables being passed in the function call, they are valid and the same both times.
Does someone have any experience with this, or can advise me on what I might be doing wrong? Is there something persisting within the function call that only clear all can remove and not clear? Save My Soul!
Yes, persistent variables can be declared by the persistent keyword.
If you want to clear only those, try
clear StartFcn
to clear all variables of the function StartFcn. A quote from the documentation:
If name is a function name, then clear name reinitializes any persistent variables in the function.
A quick thing to try would be clear mex inbetween simulations - this should clear all the mex code from matlab.
Other questions to think about..
Can you call the fortran interface directly from the matlab command line two times in a row?
I believe that using a m-file sfunction to call fortran in simulink is quite inefficient. Possibly consider writing your own fortran or C sfunction to interface to the code and compile in directly?
in case you're using LoadLibrary to load fortran code compiled into a dll, are you calling FreeLibrary in the mdlTerminate function?
Hope some of this helps.
I would try to put a clear all inside the function that you are calling in the StartFcn Callback.
So let's say your function is:
function [out] = nameoffunction(a,b,c)
%do calculation with a,b,c
d = a + b + c;
%output out
out = d;
assignin('base','out',d)
clear all
And you can call the function:
nameoffunction(a,b,c)
Let me know if it changes something. If this works, you could try other clear command but inside the function.
I am currently working on a tool written in M-Script that executes a set of checks on a given simulink model. This tool does not compile/execute the model, I'm using find_system and get_param to retrieve all the information I need in order to run the routines of my tool.
I've reached a point where I need to determine whether a certain block has direct-feedthrough or not. I am not entirely sure how to do this. Two possible solutions come to mind:
A property might store this information and might be accessible via get_param. After investigating this, I could not find any such property.
Some block types have direct-feedthrough (Sum, Logic, ...), some other do not (Unit Delay, Integrator), so I could use the block type to determine whether a block has direct-feedthrough or not. Since I'm not an experienced Simulink modeller, I'm not sure if its possible to tell whether a block has direct-feedthrough by solely looking at its block type. Also, this would require a lookup table including all Simulink block types. An impossible task, since additional block types might get added to Simulink via third party modules.
Any help or pointers to possible solutions are greatly appreciated.
after some further research...
There is an "official solution" by Matlab:
just download the linked m-file
It shows that my idea was not that bad ;)
and for the record, my idea:
I think it's doable quite easily. I cannot present you some code yet, but I'll see what I can do. My idea is the following:
programatically create a new model
Add a Constant source block and a Terminator
add the Block you want to get to know the direct feedthrough ability in the middle
add_lines
run the simulation and log the states, which will give you the xout variable in the workspace.
If there is direct feedthrough the vector is empty, otherwise not.
probably you need to include some try/catch error catching for special cases
This way you can analyse a block for direct feedthrough by just migrating it to another model, without compiling your actual main model. It's not the fastest solution, but I can not imagine that performance matters that much for you.
Here we go, this script works fine for my examples:
function feedthrough = hasfeedthrough( input )
% get block path
blockinfo = find_system('simulink','Name',input);
blockpath = blockinfo{1};
% create new system
new_system('feed');
open_system('feed');
% add test model elements
src = add_block('simulink/Sources/Constant','feed/Constant');
src_ports = get_param(src,'PortHandles');
src_out = src_ports.Outport;
dest = add_block('simulink/Sinks/To Workspace','feed/simout');
dest_ports = get_param(dest,'PortHandles');
dest_in = dest_ports.Inport;
test = add_block(blockpath,'feed/test');
test_ports = get_param(test,'PortHandles');
test_in = test_ports.Inport;
test_out = test_ports.Outport;
add_line('feed',src_out,test_in);
add_line('feed',test_out,dest_in);
% setup simulation
set_param('feed','StopTime','0.1');
set_param('feed','Solver','ode3');
set_param('feed','FixedStep','0.05');
set_param('feed','SaveState','on');
% run simulation and get states
sim('feed');
% if condition for blocks like state space
feedthrough = isempty(xout);
if ~feedthrough
a = simout.data;
if ~any(a == xout);
feedthrough = ~feedthrough;
end
end
delete system
close_system('feed',1)
delete('feed');
end
When enter for example 'Gain' it will return 1, when you enter 'Integrator' it will return 0.
Execution time on my ancient machine is 1.3sec, not that bad.
Things you probably still have to do:
add another parameter, to define whether the block is continuous or discrete time and set the solver accordingly.
test some "extraordinary" blocks, maybe it's not working for everything. Also I haven implemented anything which could deal with logic, but actually the constant is 1 so it should work as well.
Just try out everything, at least it's a good base for you to work on.
A famous exception is the StateSpace Block which can have direct feedthrough AND states. But there are not sooo much standard blocks with this "behaviour". If you also have to deal with third party blocks you could get into some trouble, I have to admit that.
possible solution for the state space: if one compares xout with yout than one can find another indicator for direct feedthrough: if there is, the vectors are not equal. If so, than they are equal. Just an example, but I can imagine that it is possible to find more general ways to test things like that.
besides the added simout block above one needs the condition:
% if condition for blocks like state space
feedthrough = isempty(xout);
if ~feedthrough
a = simout.data;
if ~any(a == xout);
feedthrough = ~feedthrough;
end
end
From the documentation:
Tip
To determine if a block has direct feedthrough:
Double-click the
block. The block parameter dialog box opens.
Click the Help button in
the block parameter dialog box. The block reference page opens.
Scroll
to the Characteristics section of the block reference page, which
lists whether or not that block has direct feedthrough.
I couldn't find a programmatic equivalent though...
Based on a similar approach to the one by #thewaywewalk, you could set up a temporary model that contains an algebraic loop, similar to,
(Note that you would replace the State-Space block with any block that you want to test.)
Then set the diagnostics to error out if there is an algebraic loop,
If an error occurs when the model is compiled
>> modelname([],[],[],'compile');
(and you should check that it is the Algebraic Loop error that has occured), then the block has direct feed though.
If no error occurs then the block does not have direct feed though.
At this point you would need to terminate the model using
>> modelname([],[],[],'term');
If the block has multiple inports or outprts then you'll need to iterate over all combinations of them.
I am a beginner of Matlab. I am trying to run this function but there seem to be a syntax error that I cannot understand. The source code is the following.
function print_trace(x)
for rowi=1:size(x,1),
for coli=1:size(x,2),
disp(x(rowi,coli))
end
end
The error encountered is the following:
??? Input argument "x" is undefined.
Error in ==> print_trace at 2
for rowi=1:size(x,1),
Any ideas?
EDIT: here is a screenshot: http://imgur.com/pwPhzhh
EDIT 2:
Trying to see if there are multiple copies running:
>> which('print_trace')
C:\Users\stablum\Dropbox\cm\print_trace.m
EDIT: solution of the problem :)
it seems that I solved the problem, my mistake was running ("play" button) the file of the function instead of just calling the function (which will load the file automatically). I still don't understand why there was this error when the file is run, but at least my problem is solved.
I suppose it is because of the way you call the function.
The error indicates that you don't give the required parameter x. Especially, you seem t o call the function with
print_trace()
or
print_trace
or
print_trace(empty_cell{:})
which leads to the effect that there is no value to be assigned to x.
I'm writing a matlab script where I'd like to know the name of the script which is one step up in the stack. The reason I need this is that I'm writing a helper script to be called to assert some basic facts about the workspace before engaging in heavier calculations, and the helper script should be able to give error messages when calling the calculation scripts.
I've tried using mfilename and dbstack, but I do not manage to get anything but the name of the helper script from them.
To explain further, I have the following scripts:
verify_base_conditions: the helper script, called on one of the first lines in
heavy_stuff_calculation and
sweet_mother_of_algorithms.
general_entry_point: a script where I gather common workflows in cells
I try to keep the entry point script as small as possible, and refactor heavier calculations (or anything that needs more than a few lines, really) into task-based, re-usable scripts. If I, from the entry point script, call sweet_mother_of_algorithms and the basic conditions for this script to run are not fulfilled, I want to see an error message like
Error: this_cool_var must be defined when running sweet_mother_of_algorithms
general_entry_point line 15
I tried using
error(['this_cool_var must be defined when running ' mdfilename])
and other similar constructs, but I couldn't make the error message say anything but verify_base_conditions.
How do I find the name of the script running one level up in the stack?
(Note: I'm not interested in finding the script running at the bottom of the stack - that will almost always be general_entry_point. I'm just interested in getting the name of the script that called verify_base_conditions.)
dbstack should work for this. I think this is an analogous set-up to yours:
a.m:
b;
b.m:
c;
c.m:
stack = dbstack;
for i=1:3
disp(stack(i));
end
When I run a;, this prints out the whole stack, including b (which I think it was you want - the second-top item on the call stack.
Alternatively, although this probably gives exactly the same result, you could throw and catch an error and look at its stack:
c.m:
try
error('What is on the call stack?');
catch e
for i=1:3
disp(e.stack(i));
end
end