I have the (very simple) equation in Maple:
x := ((1 + ((-4.5) + (-2.6))))
However, although everything should be correct, I get the following error message by Maple: Error, "-" unexpected.
If I remove the minus sign in front of the 4.5, the error disappears and x is calculated as expected. If I remove the minus sign in front of the 2.6 however, the error persists.
Note: I have to work with equations like this, i.e. I want to be able to use such equations with redundant braces (removing unneeded braces is not an option for my application).
Question: What is happening here? And how can I fix that error?
Edit: Maple Version is 16, Win 7, problem exists in both 2D math mode and 1D plain text maple input entered via the standard GUI (input mode doesn't seem to make any difference).
I found out that the problem apparently only exists in document mode. There, it doesn't matter if 1D or 2D Maple Input is used, it always gives an error for the above posted equation. It is maybe also related to floating point tokens only, as the error also disapears when using -4 instead of -4.5.
When using worksheet mode instead of document mode, the error also doesn't appear anymore, so I will just worksheet mode instead of document mode as a workaround.
Related
In MatLab (R2015a), I want to style the title of my plots using latex.
This is working fine for some functions, but not if there's a power in the equation.
The below code works, and shows a formatted title to the right, and an unformatted title to the left.
It shows the warning:
Warning: Error updating Text.
String must have valid interpreter syntax: y = x^2
syms x y
eq = y == x^2;
subplot(1,2,1)
ezplot(eq)
title(latex(eq),'interpreter','latex')
eq = y == x+2;
subplot(1,2,2)
ezplot(eq)
title(latex(eq),'interpreter','latex')
EDIT:
I just found out I can get it to work by appending $ on both sides. But it seems weird that I would have to do this.
So this works:
title(strcat('$',latex(eq),'$'),'interpreter','latex')
Solution
The problem can be solved easily by adding $-signs before and after the generated LaTeX-expression. So you can change your «title-lines» to:
title(['$',latex(eq),'$'],'interpreter','latex')
An alternative is to use strcat as proposed in your question.
Explanation
Since you basically answered the question yourself already, I'm going to explain why it happened. Hopefully after reading this, it's no longer 'weird' behaviour. If you choose to use the LaTeX-interpreter in Matlab, you really get a LaTeX-interpreter. This means that the provided string must be valid LaTeX-syntax.
Using ^ outside a math-environment is considered invalid syntax because it is a reserved character in LaTeX. Some interpreters automatically add the $ before and after in this case, but throw a warning at the same time.
The output of the latex-function in Matlab is provided without the $-signs. This way you can combine outputs and concatenate if needed without creating a mess with $-signs.
To change to the math-environment in LaTeX you can use the already mentioned shortcut $...$. An alternative way is to use \begin{math} your_equation \end{math}. It produces the same result for your equations and can be used here for demonstration purposes. The following line would do the same job, but is a bit longer to write:
title(['\begin{math}',latex(eq),'\end{math}'],'interpreter','latex')
Now, the reason why only one of your equations is displayed correctly, lies in the invalid character ^ in y = x^2. Matlab then chooses interpreter none and therefore displays the string unformatted. The +-sign in y = x + 2 is valid outside a math-environment, so it gets displayed correctly (but is not interpreted in a math-environment).
I'm trying to write a bit of code of to make MATLAB scatter plots from variables in a structure. I want to give the code the name of the structure (there will be many of these structures) and then get it to make a scatter plot of two variables. When I try the code below I get an error message saying, "??? Error: File: make_graphs.m Line: 6 Column: 9
The input character is not valid in MATLAB statements or expressions."
str2stuct= input('Please enter the string for the struct e.g. TMB_RUN_1_data:');
test1=strcat(str2stuct,'.NDROP_max');
test2=strcat(str2stuct,'.input_kappa');
scatter($(test2), $(test1))
I thought that the error message probably meant that I was using the dollar sign in a way which MATLAB doesn't approve of (I've yet to find much use for $ in MATLAB).
I tried it like this:
str2stuct= input('Please enter the string for the struct e.g. TMB_RUN_1_data:');
test1=strcat(str2stuct,'.NDROP_max');
test2=strcat(str2stuct,'.input_kappa');
scatter((test2),(test1))
And got this error:
"??? Error using ==> scatter at 51
Must supply X and Y data as first arguments.
Error in ==> make_graphs at 6
scatter((test2),(test1)) "
I tried it with changing the last line as shown below but got the same error as with the brackets:
scatter(test2,test1)
If I use the literal name as below it works fine.
scatter(TMB_RUN_1_data.NDROP_max,TMB_RUN_1_data.input_kappa)
I've tried a bunch of other things but I am not getting it. I've tried the mathworks pages on scatter but there are no examples that are close to what I am doing. I am really really stuck.
EDIT: I have found a solution but I am aware that this is not considered best practice. If you can simply explain how to do this better that would be good. Answers should be aimed at a moron in a hurry, not an experienced programmer.
Making this the last line works:
scatter(eval(test2),eval(test1))
I am aware that 'eval' is frowned upon and so this probably isn't a good long term answer, works for now. This seems to be the way to get MATLAB to actually read the contents of the strings test1 and test2 into the lines in question.
I spent a couple of hours debugging a problem that I would have thought would have been a syntax error.
a = zeros(3);
for i=1:1size(a,2) % note the missing colon between 1 and size(a,2)
i
end
The following only displays
ans = 3
1
Essentially, it seems Matlab/Octave parses the above as:
for i=1:1
size(a,2)
i
end
Note however that
i=1:1size(a,2)
produces a syntax error. Is there a good reason that Matlab/Octave has this for loop syntax? Is there something that it's supposed to make easier? Just curious if anyone else has any thoughts about it. Thanks.
It is indeed a bit of a surprise that Matlab's syntax allows this. I don't know why this is allowed. One reason might be to allow for-loops on one line:
>> for i=1:3 disp(i);end
1
2
3
But interestingly, removing the space is not allowed:
>> for i=1:3disp(i);end
for i=1:3disp(i);end
|
Error: Unexpected MATLAB operator.
This reason for this is probably that a number followed by d is another way of writing a floating point number (3d10 == 3e10), so the parser/tokenizer initially thinks you define a number, but then gets confused when it sees the i. Daniel's example with fprintf does work, since a number followed by an f is not a valid number, so the tokenizer understands that you started a new token.
I guess that many years ago (>30?), when they defined matlab's syntax, they did not foresee that this could introduce this kind of hard-to-spot problems. I guess matlab was originally written by engineers for engineers, and not by someone who knows how to design a general purpose programming language. Other languages like C or Python use punctuation to separate loop conditions from loop body, so there is no ambiguity. I don't know if it is still possible to correct Matlab's syntax, since it might break old code that relies on the current behavior.
At least, if you use a recent version of Matlab, the editor warns for various problems in your code. Paying attention to the small red dashes in the right hand border could have saved you a few hours of debugging time (but maybe you were using octave). I try to make it a habit to fix all the warnings it indicates. For your code, it shows the following:
Your code is equivalent to
a = zeros(3);
for i=1:1
size(a,2)
i
end
There are some places where everyone would use newline or white space, but the parser itself does not require.
A minimal loop:
for i=1:3fprintf('%d',i),end
but I recommend to use at least a comma seperated version, everything else is horrible to read:
for i=1:3,fprintf('%d',i),end
I am having problem when I try to store rmabackadj function's output to a variable. The function works properly when no output variable is assigned. This function is part of bioinformatics toolbox.
So the issue is when I try to run the following it works properly:
rmabackadj(myprobeData.PMIntensities)
But when I try to run the following I get an error:
>> A = rmabackadj(myprobeData.PMIntensities)
Warning: Colon operands must be real scalars.
> In rmabackadj>findMaxDensity at 255
In rmabackadj at 164
Error using ksdensity>parse_args (line 162)
X must be a non-empty vector.
Error in ksdensity (line 114)
[axarg,yData,n,ymin,ymax,xispecified,xi,u,m,kernelname,...
Error in rmabackadj>findMaxDensity (line 255)
[f, x] = ksdensity(z, min(z):(max(z)-min(z))/npoints:max(z), 'kernel', 'epanechnikov');
Error in rmabackadj (line 164)
mu = findMaxDensity( o(o < mu));
I searched for it online as well, but I couldn't find any result. Does anybody have any idea about the cause of this error?
PS: When I assign ans variable to a new variable, it is properly assigned.
A = ans
I'm pretty sure this is a bug.
Firstly, the reason it errors only when you supply an output argument is because there's an internal switch in the function that calculates different things based on nargout. That's an odd design, but not necessarily a bug.
Internal to rmabackadj there are two subfunctions findMaxDensity and findMaxDensity2. The main routine calls findMaxDensity, which is supposed to find an initial guess for the parameter mu. However (when I run the documentation example that you mention in your comment), it finds a terrible guess right on the edge, leading to an error.
When I edit the file to call findMaxDensity2 rather than findMaxDensity, it seems to produce a reasonable guess, and runs fine with no error. I can't vouch for whether the guess is actually "correct", but it seems reasonable to me, and it's only functioning as an initial guess to start off a better estimation process. (NB if you do this yourself, make sure to save a copy of the old version first).
I would guess that this is a bug, either that findMaxdensity is generating an unusually poor guess that should be caught, or that really it should be calling findMaxDensity2 and the code has not been updated to call a new subfunction.
Either way, I would report it to MathWorks.
PS I am running MATLAB R2011b. Check first if the issue has been fixed, or behaves differently, in more recent versions.
Mathworks confirmed this bug and issued a work around for it and mentioned this may be fixed in future releases.
One possible workaround is to add the following conditional at line 163 of rmabackadj function
% estimate mu from left-of-the-mode data
if any(o < mu)
mu = findMaxDensity( o(o < mu));
end
The bug for N<1000 samples has been confirmed as well but no work around has been issued yet.
I will update the thread if the work around for N<1000 samples bug.
I tried to plot graphs on MATLAB using GraphViz, using this GraphViz interface.
I keep getting this error:
>> [x,y]=draw_dot(G)
??? Attempted to access node_pos(2); index out of bounds because numel(node_pos)=1.
Error in ==> dot_to_graph at 94
y(lst_node) = node_pos(2);
Error in ==> draw_dot at 30
[trash, names, x, y] = dot_to_graph(tmpLAYOUT); % load NEATO layout
Whats really bugging me is that it worked great before (on my old computer).
Any idea how to solve this problem?
After debugging, I find the solution.
Just find the line 92 in dot_to_graph.m, as written:
[node_pos] = sscanf(line(pos_pos:length(line)), ' pos = "%d,%d"')';
Change the %d,%d to %f,%f. Because there are float numbers in the dot file.
This is difficult to answer completely since you are not giving us the G you are using, so we can't reproduce your problem directly; I'll attempt to answer anyhow "on the dry":
The error messages you get mean that the temporary DOT files created by neato in draw_dot can not be read properly; a line in the dot file which is parsed by dot_to_graph using the format string pos = "%d,%d" is expected to contain two numbers, e.g pos ="42,3", but MATLAB's sscanf only reads one number from that line.
Is it possible that your new computer uses a different language setting, i.e. using a decimal comma instead of a decimal point? This might cause Matlab to read the two numbers as one, not sure how sscanf adapts to local decimal point settings.
Otherwise, are you still using the same version of neato as before? Could it be that its output format has changed in some way?
The best way to find out might be to set a debugging break point in the offending line 94 ([node_pos] = sscanf(line(pos_pos:length(line)), ' pos = "%d,%d"')';) and check what line(pos_pos:length(line)) evaluates to.