I've did my code like that :
r= randper(3)
switch num2str(r(i))
case '1' F1=func1(var1);
case '2' F2=func2(var2);
case '3' F3=func3(var3);
otherwise disp('error');
end
In Matlab, i coudn't find the way to concatenate r with "func" and that could e read as a function not as string
Usually in other langage I could do it like that (it's just an example)
r= randper(3)
F+r(i)=func+r(i)(var+r(i))
Q: How could I shorten my code in one line ?
Thanks !
Ok, there's two ways of doing this: the quick way, and the nice way.
The quick way uses eval which evaluates a string as though it were m-code.
r= randper(3)
eval('F' + num2str(r(i)) + ' = func' + r(i) + '(var' + r(i) + ')');
The nice way creates an array of function pointers and then calls those:
func{1} = #func1;
func{2} = #func2;
func{3} = #func3;
r = randperm(3);
F{r(i)} = func{r(i)}(var(r(i)));
The above method helps avoid the myriad of issues that can crop up when you have used eval.
Related
So, I have a really long symbolic exrpression in Matlab that I want to copy/paste into a JavaScript-code to animate a numerical solution for it. The problem is that some places in my code i get exponents (mostly ^2), when I'd rather have Matlab express it as A*A.
I have mulitple (and different) expressions like
cos(th2t)^2
That I would rather have expressed as
cos(th2t)*cos(th2t)
Any way I can do this? The alternative is to use a text editor afterward and search for powers of 2 and replace it, but there are multiple different expressions, so that would take some time...
This is an example of one of the exrpressions I end up with:
(J31*(2*ddth2t*cos(th1t) - 2*w12*w13 - 4*dth1t*dth2t*sin(th1t) - 4*dth2t*w13*sin(th1t) + dth1t^2*sin(2*th2t)*cos(th1t) - w12^2*sin(2*th2t)*cos(th1t) + w13^2*sin(2*th2t)*cos(th1t) + 2*dth2t*w11*sin(2*th2t) + 2*w12*w13*cos(th2t)^2 + ddth1t*sin(2*th2t)*sin(th1t) + 4*dth1t*dth2t*cos(th2t)^2*sin(th1t) + 2*dth1t*w13*sin(2*th2t)*cos(th1t) + 4*dth2t*w13*cos(th2t)^2*sin(th1t) + w11*w12*sin(2*th2t)*sin(th1t) + 4*dth1t*w12*cos(th1t)^2*cos(th2t)^2 - 2*dth1t*w11*sin(2*th1t)*cos(th2t)^2 - 2*dth2t*w11*sin(2*th2t)*cos(th1t)^2 + 2*w12*w13*cos(th1t)^2*cos(th2t)^2 - w11*w13*sin(2*th1t)*cos(th2t)^2 - 4*dth2t*w12*cos(th1t)*cos(th2t)*sin(th1t)*sin(th2t)))/(2*(J11 + J31))
Steve's answer should work fine if you want to rely on the ** operator. However, since that operator is not officially supported, and that solution doesn't directly answer the OP's question, here is a function that can expand out the exponents in a symbolic expression.
function [ text ] = remove_powers( exp )
%Cleans the powers from T, and return expanded text representation
% Define functions
enclose =#(t) ['(' t ')'];
expand_pow=#(b,p) strjoin(strcat(cell(1,p),enclose(char(b))),'*');
count_pow=#(s) arrayfun(#(k) count(char(s(k)),'^'), 1:length(s));
sym2str = #(s) strrep(char(s), ' ', '');
% Check for fractions
[N,D]=numden(exp);
if ~isequal(D,sym(1))
% pass up the num and den
text = [remove_powers(N) '/' enclose(remove_powers(D))];
else
% Split a into subterms
Ts = children(exp);
% Clean children
has_pow=count_pow(Ts)>0;
text = sym2str(exp);
if sum(count_pow(Ts))<count_pow(exp)
% We have removed a power, clean it, expand it, and pass up
text = expand_pow(remove_powers(Ts(1)),Ts(2));
else
% Just clean the unclean children and pass up
for t=Ts(has_pow)
text = strrep(text,sym2str(t),remove_powers(t));
end
end
end
end
The function uses the children function in Matlab to recursively clean each subexpression and replace it (as text) in the parent. This method is better than using regex because it avoids the issue of parsing the syntax, as Steve mentioned in the comment with respect to cos(x^2+2*y)^2.
Which makes for a good example:
syms x y real
exp = cos(x^2+2*y)^2;
cleaned_exp = remove_powers(exp)
Outputs: (cos(2*y+(x)*(x)))*(cos(2*y+(x)*(x)))
Notice that since Matlab is doing the parsing, there was no need to parse the order of precedence for the '^' operators, which could be difficult to accomplish with regex.
To test the OP's example:
syms ddth1t dth1t th1t ddth2t dth2t th2t w11 w12 w13 J11 J31 real
exp = (J31*(2*ddth2t*cos(th1t) - 2*w12*w13 - 4*dth1t*dth2t*sin(th1t) - 4*dth2t*w13*sin(th1t) + dth1t^2*sin(2*th2t)*cos(th1t) - w12^2*sin(2*th2t)*cos(th1t) + w13^2*sin(2*th2t)*cos(th1t) + 2*dth2t*w11*sin(2*th2t) + 2*w12*w13*cos(th2t)^2 + ddth1t*sin(2*th2t)*sin(th1t) + 4*dth1t*dth2t*cos(th2t)^2*sin(th1t) + 2*dth1t*w13*sin(2*th2t)*cos(th1t) + 4*dth2t*w13*cos(th2t)^2*sin(th1t) + w11*w12*sin(2*th2t)*sin(th1t) + 4*dth1t*w12*cos(th1t)^2*cos(th2t)^2 - 2*dth1t*w11*sin(2*th1t)*cos(th2t)^2 - 2*dth2t*w11*sin(2*th2t)*cos(th1t)^2 + 2*w12*w13*cos(th1t)^2*cos(th2t)^2 - w11*w13*sin(2*th1t)*cos(th2t)^2 - 4*dth2t*w12*cos(th1t)*cos(th2t)*sin(th1t)*sin(th2t)))/(2*(J11 + J31));
cleaned_exp = remove_powers(exp);
isequal(sym(cleaned_exp),exp) % This should be 1
count(cleaned_exp,'^') % This should be 0
As expected, the new expression is equivalent to the original, but has no '^' symbols.
This answer suggests that you could call the exponential operator in Javascript with e.g. A**2. As such you could replace all instances of ^ with **.
(Solution from comments)
I would like to have short-hand form about many parameters which I just need to keep fixed in Matlab 2016a because I need them in many places, causing many errors in managing them separately.
Code where the signal is 15x60x3 in dimensions
signal( 1:1 + windowWidth/4, 1:1 + windowWidth,: );
Its pseudocode
videoParams = 1:1 + windowWidth/4, 1:1 + windowWidth,: ;
signal( videoParams );
where you cannot write videoParams as string but should I think write ":" as string and everything else as integers.
There should be some way to do the pseudocode.
Output of 1:size(signal,3) is 3 so it gives 1:3. I do not get it how this would replace : in the pseudocode.
Extension for horcler's code as function
function videoParams = fix(k, windowWidth)
videoParams = {k:k + windowWidth/4, k:k + windowWidth};
end
Test call signal( fix(1,windowWidth){:}, : ) but still unsuccessful giving the error
()-indexing must appear last in an index expression.
so I am not sure if such a function is possible.
How can you make such a int-string-int input for the matrix?
This can be accomplished via comma-separated lists:
signal = rand(15,60,3); % Create random data
windowWidth = 2;
videoParams = {1:1+windowWidth/4, 1:1+windowWidth, 1:size(signal,3)};
Then use the comma-separated list as such:
signal(videoParams{:})
which is equivalent to
signal(1:1+windowWidth/4, 1:1+windowWidth, 1:size(signal,3))
or
signal(1:1+windowWidth/4, 1:1+windowWidth, :)
The colon operator by itself is shorthand for the entirety of a dimension. However, it is only applicable in a direct context. The following is meaningless (and invalid code) as the enclosing cell has no defined size for its third element:
videoParams = {1:1+windowWidth/4, 1:1+windowWidth, :};
To work around this, you could of course use:
videoParams = {1:1+windowWidth/4, 1:1+windowWidth};
signal(videoParams{:},:)
For example, imagine that I've in my workspace 100 variables whoes names range from var_1 to var_100. Now I want to create a matrix using all the variable starting with the name 'var_'.
I know I could try to list all the variables, but that would be ineficient and long:
A = [var_1 var_2 ... var_100]
Is there a better way to do complish this?
While this is probably (most definitely) not a good idea, here is what you can do:
varstr = 'A = ['
for ii = 1:100
varstr = [varstr, ' var_', num2str(ii)];
end
varstr = [varstr, '];']
eval(varstr)
The eval function lets you execute a string of matlab code. Therefore, you just need to generate a string that constructs the array, then pass it to eval. Fortunately, this is pretty easy:
eval([ 'A = [' sprintf('var_%d, ', 1:100) ']']);
It might be a little clearer if you actually do the assignment outside of the eval, like so
A = eval([ '[' sprintf('var_%d, ', 1:100) ']']);
Note that the string here has an extra trailing comma. That doesn't seem to be a problem, at least on 2014b.
If you don't know the total number of variables, you can get them with the who command. This returns a cell array of strings, which you'd then reformat and pass to eval, like so
my_variables = who('var_*');
% You may want to sort (re-order, take a subset of) my_variables here
str_to_run = '['
for ii=1:length(my_variables)
str_to_run = [str_to_run, my_variables{ii}, ',']
end
I am working in Matlab. I have defined:
a(1).x=1;
a(1).y=2;
a(1).z.w=3;
a(2).x=4;
a(2).y=5;
a(2).z.w=6;
I am now trying to add the fields in the two structures a(1) and a(2) such that I get:
c.x = 5;
c.y = 7;
c.z.w = 9;
Any idea how I can do this in an elegant way? Note that in the original problem the structures have many more fields (around 50).
Thank you very much in advance!
José
Here is a solution, for any depth of struct
The code of the script (or MATLAB command)
a(1).x=1;
a(1).y=2;
a(1).z.w=3;
a(2).x=4;
a(2).y=5;
a(2).z.w=6;
c=a(1);
c = returnStruct(c, a(2));
%{
you can also sum any amount of structs
for i=2:length(a)
c=returnStruct(c, a(i));
end
%}
with the recursive function
function rs = returnStruct(s,a)
fn = fieldnames(s);
for i=1:length(fn)
if isstruct(s.(fn{i}))
s.(fn{i}) = returnStruct(s.(fn{i}), a.(fn{i}));
else
s.(fn{i}) = s.(fn{i})+a.(fn{i});
end
end
rs = s;
end
I tested it for deeper levels of structs and it worked perfectly. Maybe, you have to adapt it slightly for your case, but this should be the way to go.
Unfortunately, any function like struct2cell only converts the first level, so you need something else.
If the deepest substructure level is 2 then this code will work:
fields=fieldnames(a);
for i=1:numel(fields)
if isstruct(a(1).(fields{i}))
fields2=fieldnames(a(1).(fields{i}));
for j=1:numel(fields2)
a(3).(fields{i}).(fields2{j})= a(1).(fields{i}).(fields2{j})+a(2).(fields{i}).(fields2{j});
end
else
a(3).(fields{i})=a(1).(fields{i})+a(2).(fields{i});
end
end
You can have a simple recursive solution
function r = sumfields(s)
if isstruct(s)
for f = fieldnames(s).'
r.(f{1}) = sumfields([s.(f{1})]);
end
else
r = sum(s);
end
end
Can I convert a symbol that is a product of products into an array of products?
I tried to do something like this:
syms A B C D;
D = A*B*C;
factor(D);
but it doesn't factor it out (mostly because that isn't what factor is designed to do).
ans =
A*B*C
I need it to work if A B or C is replaced with any arbitrarily complicated parenthesized function, and it would be nice to do it without knowing what variables are in the function.
For example (all variables are symbolic):
D = x*(x-1)*(cos(z) + n);
factoring_function(D);
should be:
[x, x-1, (cos(z) + n)]
It seems like a string parsing problem, but I'm not confident that I can convert back to symbolic variables afterwards (also, string parsing in matlab sounds really tedious).
Thank you!
Use regexp on the string to split based on *:
>> str = 'x*(x-1)*(cos(z) + n)';
>> factors_str = regexp(str, '\*', 'split')
factors_str =
'x' '(x-1)' '(cos(z) + n)'
The result factor_str is a cell array of strings. To convert to a cell array of sym objects, use
N = numel(factors_str);
factors = cell(1,N); %// each cell will hold a sym factor
for n = 1:N
factors{n} = sym(factors_str{n});
end
I ended up writing the code to do this in python using sympy. I think I'm going to port the matlab code over to python because it is a more preferred language for me. I'm not claiming this is fast, but it serves my purposes.
# Factors a sum of products function that is first order with respect to all symbolic variables
# into a reduced form using products of sums whenever possible.
# #params orig_exp A symbolic expression to be simplified
# #params depth Used to control indenting for printing
# #params verbose Whether to print or not
def factored(orig_exp, depth = 0, verbose = False):
# Prevents sympy from doing any additional factoring
exp = expand(orig_exp)
if verbose: tabs = '\t'*depth
terms = []
# Break up the added terms
while(exp != 0):
my_atoms = symvar(exp)
if verbose:
print tabs,"The expression is",exp
print tabs,my_atoms, len(my_atoms)
# There is nothing to sort out, only one term left
if len(my_atoms) <= 1:
terms.append((exp, 1))
break
(c,v) = collect_terms(exp, my_atoms[0])
# Makes sure it doesn't factor anything extra out
exp = expand(c[1])
if verbose:
print tabs, "Collecting", my_atoms[0], "terms."
print tabs,'Seperated terms with ',v[0], ', (',c[0],')'
# Factor the leftovers and recombine
c[0] = factored(c[0], depth + 1)
terms.append((v[0], c[0]))
# Combines trivial terms whenever possible
i=0
def termParser(thing): return str(thing[1])
terms = sorted(terms, key = termParser)
while i<len(terms)-1:
if equals(terms[i][1], terms[i+1][1]):
terms[i] = (terms[i][0]+terms[i+1][0], terms[i][1])
del terms[i+1]
else:
i += 1
recombine = sum([terms[i][0]*terms[i][1] for i in range(len(terms))])
return simplify(recombine, ratio = 1)