The image shows my problem (link)
I want to use that to do a Jacobian for a Multivariable method of aproximation. So There is a way to use that easily? or I have to put manually the partial derivatives like new functions?
I'm sorry for my english.
Firstly, you dont have to use images here, you can easily insert code pieces. As for your problem, i didnt understand it. Im sure you already know that you can define a Jacobian matrix function of 2 variables:
j2_fun(f1,f2):=[[derivative(f1,x),derivative(f1,y)][derivative(f2,x),derivative(f2,y)]]
... and call it later with specific arguments, and evaluate for some x,y:
g1:=x^2+y^2
g2:=x^2-y^2
d2:=j2_fun(g1,g2)
d2|x=3 and y=1
So staring from here, please define more clearly what would you like to do with this.
Related
I have the following function that I wish to solve using fzero:
f = lambda* exp(lambda^2)* erfc(lambda) - frac {C (T_m - T_i)}/{L_f*sqrt(pi)}
Here, C, T_m, T_i, and L_f are all input by the user.
On trying to solve using fzero, MATLAB gives the following error.
Undefined function or variable 'X'.
(where X are the variables stated above)
This error is understandable. But is there a way around it? How do I solve this?
This is answered to the best of my understanding after reading your question as it's not really clear what you are exactly trying and what you want exactly.
Posting the exact lines of code helps a big deal in understanding(as clean as possible, remove clutter). If then the output that matlab gives is added it becomes a whole lot easier to make sure we answer your question properly and it allows us to try it out. Usually it's a good idea to give some example values for data that is to be entered by the user anyway.
First of to make it a function it either needs a handle.
Or if you have it saved it as a matlab file you generally do not want other inputs in your m file then the variable.
So,
function [out]=yourfun(in)
constants=your values; %you can set a input or inputdlg to get a value from the user
out= something something, your lambda thingy probably; %this is the equation/function you're solving for
end
Now since that is not all that convenient I suggest the following
%declare or get your constants here, above the function makes it easier
syms lambda
f = lambda* exp(lambda^2)* erfc(lambda) - frac {C (T_m - T_i)}/{L_f*sqrt(pi)};
hf=matlabFunction(f); %this way matlab automatically converts it to a function handle, alternatively put #(lambda) in front
fzero(hf,x0)
Also this matlab page might help you as well ;)
I want to restrict the variable that I use as input for a matlab function block, it must be only able to increase.
To achieve that i have tried to compare the variable and the previous sample of it in a matlab function, but i don't know how to create two inputs. To solve that i've tried to use a mux, but then i get an error. And google doesn't give me an explanation how to use a mux signal as input for a matlab function.
So that leaves me here with this low-level question.
Thanks in advance for your help and time. Cheers.
To use multiple variables in a function, you need to modify your function declaration at the first line of your function. The reference syntax is:
function [y1,...,yN] = myfun(x1,...,xM)
where x1 through xM are inputs. Your declaration with two inputs might look something like:
function [returnValue] = hasIncreased(previousSample, variable)
See the Matlab Function Documentation for more information.
I keep getting this error. I received this error after I corrected for logical integer error. The only way I could think of programming this was defining the initial value and then start euler's method at the next t value since it uses the previous solution to find the next one. But by doing this I am getting this error? I'm unsure how to fix it. I tried to end one step from my final value but that didn't work either. Thanks for the help. For the problem we had to create the function and call it. I was initially using n=8.
function [exeuler] = pb3(n)
%using explicit euler to solve ODE with input n and outputting exeuler as
%the answer
%n=steps t,y are initial conditions
h=3/n;
t=logical((1+h):h:4);
back=logical(t-h);
exeuler(1)=2; %defines the initial value
exeuler(t)=exeuler(back)+h*(t.^2-(2*exeuler(back)/t));
end
Well, I am sorry, but you haven't showed much of effort. For the future, please provide the complete code (i.e. with example function and so on). This is very unclear.
I think your problem is in these lines:
t=logical((1+h):h:4);
exeuler(t)=exeuler(back)+h*(t.^2-(2*exeuler(back)/t));
cause t is a vector. You are calling vector with non-integer values as index. Then, I guess, you get the wrong amount of exeuler(t)'s which leads to the error.
And for-loop is missing, isn't it? Because you don't use the Euler method stepwise andd therefore f(t+1) doesn't really depend on f(t).
So, my advice in general would be not to correct this error, but to rethink your algorithm.
I am currently having an equation that contains 4~5 variables, and I am unfamiliar with matlab. I want to see how a variable change with the other variable fixed (might assign them some value). Maying graphing them out will help. I found it cumbersome to work in the main GUI in matlab, this is mainly after I type in my equation, I didn't know if the expression is what I want because of missing brackets, etc.
Recently I found mudpad, it is better because it will show you the expression in pretty form. I am wondering is there any other tool-box that is more suitable for my intention?
Update:
Ps=1;
Pr=1;
Pd=1;
g=0.25;
d1=1;
d2=1;
n=0.18;
Yr = #(x)(Ps)/(d1*((Pd*g^2)/d2 + (n*(x- 2))/(x- 1)));
Yr_=ezplot(Yr,0,1);
There is actually 4 more equations to plot and I am only posting one of them.
http://www.mathworks.com/help/techdoc/ref/fftshift.html
If you check that link - thats what I want to do in the first picture - swap quadrants of a matrix.
However, I cant seem to think of a good way to do this without having several loops to pull out the relevant sub-matrices.
I need it to work with MxN matrices, where M and N can be any combination of even and odd.
Thanks
The following should work
sz = ceil(size(A)/2)
A = A([sz(1)+1:end, 1:sz(1)], [sz(2)+1:end, 1:sz(2)])
That only works for 2d matrices, but can be easily generalized to the Nd case.
If you enter type fftshift.m at MATLAB's command line, you'll see the source code for MATLAB's implementation of the function (use edit fftshift.m if you want to view it in the editor with syntax highlighting). I'm not posting the code here, as it is copyrighted. However, you can try it on your machine and re-implement the same in C. Its up to you to figure out the license terms etc, if you're into any of that.