I want to ask about function M-file in MATLAB: if I want input from the user, how do I do that?
Can I write the input directly in the function M-file?
Or do I have to write an input statement in a script file and return to the function file to write another statement?
As Luis mentioned, the input function (documentation) prompts the user and then receives input. As far as I know, it will work fine whether in a function or in a script. If you find that it doesn't, post the code so folks can take a look at it.
input will treat what the user types as if you had typed it at a matlab command line. For example, if your code says
count=input('Enter a count')
and the user enters 3*5, the value of count will be 15. To get exactly "3*5", use input('Prompt','s') instead.
Related
I want to publish my assignment with matlab.
At the start of the program, I want to print the code of my scripts to show the teacher what my functions do.
How can I do this?
So far the best way I do this is by making a dummy call at the start without ending the function call with ";"
However I'd really like to just print the code at the start.
You can use the type command:
type fileName.m
This will print the code, similarly to creating a variable and not using a semicolon to see the value of that variable.
There are tools in MATLAB for publishing code. You could conceivably even write a report in MATLAB code and publish that! Take a look at publishing MATLAB code and the documentation of the function publish
If you are interested to print particular lines from a .m file, look into dbtype.
Illustration from Mathworks site linked above. This:
becomes this:
I recently started using Live editor in MATLAB and I inserted a function inside it. But, apparently, I cannot execute that particular section of code where I type function. Even the section break disappears.
Is it that using function is not suitable for live editor?
Apparently the MATLAB parser did not join the 20th century until partway through 2016, and could not interpret function definitions in scripts (live or otherwise) until R2016b. In the web-based docs, there is a notice at Add Functions to Scripts, but it took me a while to find this out because the builtin docs in R2016a or earlier do not explicitly contain this information. It is implied by the tutorials that tell you to create a new file for each function (which to me, a python programmer, sounds more like strange advice than a restriction).
Trying to define a function in a live script gives confusing errors. For example, if you create a cell with this content:
function y = myfunc(x)
y = 2*x;
end
It will underline the keyword function with a popup error that reads:
Parse error at FUNCTION: usage might be invalid MATLAB syntax.
Might be? Whom shall I ask? Upon running the cell, it prints an error after the first line:
All functions in a script must be closed with an end.
I eventually made this discovery myself thanks to a helpful message if the first thing you happen to do in a new empty live script is to start typing function on the first line; as soon as you hit the spacebar a message pops up at the top saying:
Functions and classes are not supported in the Live Editor. To continue, save the file as a plain text code file (.m).
It should work as when you add a function inside a script. For example, like this:
What function are you exactly trying to code?
On the Ti-84 and Ti-89, I know that one can use "Define" to define a function with multiple variables. However, is there a way to use "Prompt" or something of the sort to define a function?
Suppose we have a very simple program that evaluates an expression (only an example):
Prompt a,b,c
Disp a^5-sqrt(c)/b
Instead of having to manually go into the Program Editor every single time to change the expression, how can we automatically Prompt the user to Define a function such as eq(a,b,c)=a^5-sqrt(c)/b?
Yes you can! Use y-variables.
Functions are stored as y-variables on the TI-84, and these variables can be accessed by going to the VARS>Y-VARS>Function... menu. Then you can prompt the user for the equation with the y-variable being the input, like this:
Prompt Y1
Keep in mind that this is a string, meaning you need quotation marks at the beginning and end of your function when putting it in as the user. This can be cumbersome, and can be avoided by using Input instead, and storing it into a String variable (found in VARS>String...) first then to a y-variable.
Input "f(a,b,c): ",Str1
Str1→Y1
I'm having troubles with my code in Matlab. I want to get the mean value of all the elements in the second column in a file, but for some reason the code does not include the last line.
My file looks like this:
And my code looks like this:
As you might already understand, my code gets the mean value of all numbers except the last one for Italy.
Any suggestions on how to proceed would be highly appreciated.
It's actually suggested by Mathworks to not use feof with fgetl loops, but to instead check whether the output is with ischar. Simply replace ~feof(fid) with ischar(line).
A side note: line is also a MATLAB function, by using it as a variable name you are shadowing the function. While it is not critical here, you should try to avoid doing this. If you try to use line the function or another function which calls line while you have a variable line in the workspace, you'll likely get an error. This is why you'll see the examples in the help use things like tline as variable names instead.
You should put
line=fgetl(fid)
to the top in the while loop.
I am defining a variable in the beginning of my source code in MATLAB. Now I would like to know at which lines this variable effects something. In other words, I would like to see all lines in which that variable is read out. This wish does not only include all accesses in the current function, but also possible accesses in sub-functions that use this variable as an input argument. In this way, I can see in a quick way where my change of this variable takes any influence.
Is there any possibility to do so in MATLAB? A graphical marking of the corresponding lines would be nice but a command line output might be even more practical.
You may always use "Find Files" to search for a certain keyword or expression. In my R2012a/Windows version is in Edit > Find Files..., with the keyboard shortcut [CTRL] + [SHIFT] + [F].
The result will be a list of lines where the searched string is found, in all the files found in the specified folder. Please check out the options in the search dialog for more details and flexibility.
Later edit: thanks to #zinjaai, I noticed that #tc88 required that this tool should track the effect of the name of the variable inside the functions/subfunctions. I think this is:
very difficult to achieve. The problem of running trough all the possible values and branching on every possible conditional expression is... well is hard. I think is halting-problem-hard.
in 90% of the case the assumption that the output of a function is influenced by the input is true. But the input and the output are part of the same statement (assigning the result of a function) so looking for where the variable is used as argument should suffice to identify what output variables are affected..
There are perverse cases where functions will alter arguments that are handle-type (because the argument is not copied, but referenced). This side-effect will break the assumption 2, and is one of the main reasons why 1. Outlining the cases when these side effects take place is again, hard, and is better to assume that all of them are modified.
Some other cases are inherently undecidable, because they don't depend on the computer states, but on the state of the "outside world". Example: suppose one calls uigetfile. The function returns a char type when the user selects a file, and a double type for the case when the user chooses not to select a file. Obviously the two cases will be treated differently. How could you know which variables are created/modified before the user deciding?
In conclusion: I think that human intuition, plus the MATLAB Debugger (for run time), and the Find Files (for quick search where a variable is used) and depfun (for quick identification of function dependence) is way cheaper. But I would like to be wrong. :-)