MATLAB load not working with variable filename

Question

I try to load a .mat file in MATLAB R2016a. However, when I make the filename variable, it fails with

Error using load Unable to read file 'filename'. No such file or directory.

The documentation for R2018a states that the filename has to be

specified as a character vector or string

which i did. I searched for similar questions on SO, but they were all due to typing errors, e.g. Error using load; Unable to read file matlab

Code for reproduction:

clear all
mat1 = magic(5);
save mat1
clear mat1
load mat1 % working
clear mat1
filename = 'mat1.mat'; % tried with/without .mat
load filename % not working

What is the cause of this error?
How to resolve it?

Could the down-voters please give a reason? It took me some time to figure this out; it was not answered here before; it is encouraged to answer own questions: https://stackoverflow.com/help/self-answer — David, Jun 29 '18 at 10:55
I didn’t downvote, but this same question has been asked very often. — Cris Luengo, Jun 29 '18 at 12:26
Thanks for the response. I must have used the wrong search terms for not finding the first two examples. The third one seems to be a different problem. — David, Jun 29 '18 at 12:48

David · Answer 1 · 2018-06-29T09:43:44.137

1

After further research I found that the documentation (R2018a) also states

load filename is the command form of the syntax. [...] Do not use command form when any of the inputs, such as filename, are variables.

This answers my second question. Use:

load(filename)

edited Jun 29 '18 at 09:43

answered Jun 29 '18 at 09:35

David

85
7

loudmummer · Answer 2 · 2018-07-01T10:26:11.583

1

The cause of this error is that the statement:

load filename

internally evaluates to:

load('filename.mat')

in order to support command-form statements statements like load mat1 in your example. It fails because the file filename.mat clearly does not exist.

The function form is always safer, in my opinion.

edited Jul 01 '18 at 10:26

answered Jun 29 '18 at 12:08

loudmummer

544
3
19

Thanks for the response. However, if this is really the cause, something like `filename = 'mat1';load filename` (without .mat) should work - but it doesn't. – David Jun 29 '18 at 12:56
1

@David `load filename` evaluates to `load('filename.mat')`; not `load('mat1.mat')` and hence it *shouldn't* work. – Sardar Usama Jun 29 '18 at 13:52
The last sentence in the answer is opinion based though – Sardar Usama Jun 29 '18 at 13:54
Yeah, @SardarUsama I made a change to that sentence. But is there any situation where the command form is safer? – loudmummer Jul 01 '18 at 10:27
If a person doesn't know the syntax, he should read the documentation. If someone is randomly trying to use a function, he shouldn't expect it safe. – Sardar Usama Jul 01 '18 at 10:30
Of course. But I meant function form is safer as opposed to the command form in terms of syntax. – loudmummer Jul 01 '18 at 10:35
No it is not. These are equally safe if a person reads the doc instead of randomly trying to use it – Sardar Usama Jul 01 '18 at 10:37
1

Right, okay. Understood. – loudmummer Jul 01 '18 at 10:40

MATLAB load not working with variable filename

2 Answers2