Here I tried to insert a value in GLKVector2Add value but the error comes expected expression missing in this line.
GLKVector2 self.position = GLKVector2Add({-200.695, 271},{-803.695, 0}); //Error - Expected expression
Try creating "GLKVector2" variables, setting them and then passing those as arguments in your call to "GLKVector2Add". It may be that the compiler simply doesn't know what to do with "{-200.695,271}" (a mix of float and integer numbers).
You must add them using GLKVector2Make.
So, your code will be:
GLKVector2 position = GLKVector2Add(
GLKVector2Make(-200.695, 271),
GLKVector2Make(-803.695, 0));
Related
I am upgrading my Matlab from 2013b to 2018b and have found out that MathWorks have made quite a few changes to the GUI's.
One problem I am having is getting the value of checkbox. The line below is the code I used to use but now it doesn't work.
if get(handles.check_perf_attr,'Value') == 1
The error message is,
Undefined operator '==' for input arguments of type 'cell'.
So I tried the line below to just get the value that is being returned and then apply some logic.
tValue = get(handles.check_perf_attr,'Value');
However tValue is 2 x 1 cell which in (1, 1) = 0 & (2, 1) = 1. I don't really understand this as surely a checkbox can only be one value true (1) or false (0)?
get returns a cell array with values when applied to an array of handles.
Thus, I think your problem is that handles.check_perf_attr contains two handles, not one.
"Dot notation is a new syntax to access object properties starting in R2014b."
so try
if handles.check_perf_attr.Value == 1
or
tValue = handles.check_perf_attr.Value;
When using vDSP to perform some speedy calculations, I often don't care about one of the output parameters. Let's say I'm finding the index of an array's maximum value:
var m:Float = 0
var i:vDSP_Length = 0
vDSP_maxvi(&array,
1,
&m,
&i,
vDSP_Length(array.count))
Ideally, I'd like to get rid of m altogether so that vDSP_maxvi fills i only. Something like:
var i:vDSP_Length = 0
vDSP_maxvi(&array,
1,
nil,
&i,
vDSP_Length(array.count))
But of course this doesn't work ("nil is not compatible with expected argument type 'UnsafeMutablePointer<Float>'"). Is there some sort of argument I can send to these kinds of methods that says "ignore this parameter"? Thanks for reading.
Except for documented cases where a null argument is accepted, you must pass a valid address. There is no argument value that tells vDSP to ignore the argument.
This code fails:
let element: Float = self.getElement(row: 1, column: j)
let multiplier = powf(-1, j+2)*element
with this error:
Playground execution failed: :140:51: error: cannot invoke '*' with an argument list of type '(Float, Float)'
let multiplier = powf(-1, j+2)*element
Bear in mind that this occurs in this block:
for j in 0...self.columnCount {
where columnCount is a Float. Also, the first line does execute and so the getElement method indeed returns a Float.
I am completely puzzled by this as I see no reason why it shouldn't work.
There is no implicit numeric conversion in swift, so you have to do explicit conversion when dealing with different types and/or when the expected type is different than the result of the expression.
In your case, j is an Int whereas powf expects a Float, so it must be converted as follows:
let multiplier = powf(-1, Float(j)+2)*element
Note that the 2 literal, although usually considered an integer, is automatically inferred a Float type by the compiler, so in that case an explicit conversion is not required.
I ended up solving this by using Float(j) instead of j when calling powf(). Evidently, j cannot be implicitly converted to a Float.
I'm attempting to make a program (for homework) which reads in a file, and then counts the number of times each word is used. For tackling the issue efficiently, I've decided to map all unique words to keys, and then increment the key value each time the word comes up.
function [] = problem2
file_open = fopen('austen.txt');
complete_string = textscan(file_open, '%s');
numel(complete_string{1,1})
unique_words = unique(complete_string{1,1});
length(unique_words);
frequency = zeros(numel(unique_words), 1);
found_frequency = containers.Map(unique_words, frequency);
for i=1:numel(complete_string{1,1})
found_frequency(complete_string{1,1}(i)) = found_frequency(complete_string{1,1}(i))+1;
end
fclose(file_open)
Sadly, this code does not work. When the line comes up to increment, I receive an error stating that "specified key type does not match the type expected for this container", which makes no sense to me - I'm using strings as the keys. Any ideas as to why I'm receiving this error?
The issue was in the use of Cell type - complete_String{1,1}(i) would actually return a Cell rather than a String (per spec, though). Wrapped it in char(*) and it worked fine.
In most OO languages, where variables may point to objects, they may also have a null value, which is highly convenient.
In Matlab, I have a function which parses a command, and then returns a cell array, or false (which is equal to zero — which is another common pattern) if it fails:
function re = parse(s)
...
if (invalid)
re = false;
return;
end
end
The problem is that when I check the result, it gives an error:
re = parse(s);
if (false == re)
Undefined function 'eq' for input arguments of type 'cell'.
I've written a function to check it without an error: strcmp('logical', class(re)) && false == re, but that seems to be really slow for use in hot areas of the code, and also inconvenient if I have to add this function to every M file I'm writing.
Using NaN is even worse, because besides throwing that error, it also isn't equal to itself.
What's a better alternative for use with this pattern?
You can use the isequal function to compare any two items without causing that error. For example:
if isequal (re, false)
%code here
end
A good alternative is to use the empty array: [] and isempty(re) to check. This doesn't throw the error.
Reference: http://www.mathworks.com.au/matlabcentral/newsreader/view_thread/148764
If you can change the function parse one solution would be to return two output arguments [re status] = parse(s), where status would be logical variable. Set it to true in case of success, and to false otherwise.
I would use the empty cell array {} if it is not a valid result otherwise. Using empty matrices is MATLAB standard (see Evgeni Sergeev's answer), but using an empty cell array instead of an empty numeric array ensures that you'll always end up with the same type of result.
If, on the other hand, the empty cell array {} is a valid result of your function, then I'd use an exception to signalize a problem:
if invalid
error('Parse:InvalidArgumentError', 'The input is invalid.');
end
Make sure to use an appropriate error ID (first argument to error) so that you can catch exactly that exception when you call the function:
try:
result = parse(something);
catch ME
if strcmp(ME.identifier, 'Parse:InvalidArgumentError')
fprintf('Ooops\n');
else
% Some other error
ME.rethrow();
end
end
I think the problem is that matlab functions don't return pointers but copies of values.
IMHO the best best approach would be to define your own "pointer" class. Inside you can define an "isNull()" command or even override comparison to produce the behavior you desire.