I want to sweep the variable Q from -.4 to +.4 and then plot the variable V for each individual value of Q.
0.188Q^2+.44*V^2*Q+.0221+V^4+(.2-1.05^2)*V^2=0
But I am not sure how to go about solving this problem, as I have never faced something like this before. Can someone please advice on how to code this?
This is job for ezplot!
As you have your function in implicit form, unless you write it in explicit form (i.e. y=..) you can not use plot. But you can use ezplot!
just do
ezplot('x.*0.188*x.^2+.44*y.^2*x+.0221+y.^4+(.2-1.05^2)*y^2',[-4 4])
Related
the variable nowT is a constant but I don't know how to fix it, it need to be a matrix
My code is:
lambda1=1.064; % unit:um
lambda2=0.532; % unit:um
T=0:500;
nowT=(4.9130+(0.1173+T.*T.*1.65e-8)/(lambda1.*lambda1-(0.212+T.*T.*2.7e-8).^2)-lambda1.*lambda1.*2.78e-2);
ne2wT=(4.5567+T.*T.*2.605E-7+(0.097+T.*T.*2.7E-8)/(lambda2.*lambda2-(0.201+T.*T.*5.4e-8).^2)-2.24E-2.*lambda2.*lambda2);
figure('name','temperature phase matching chart','NumberTitle','off')
plot(T,nowT,T,ne2wT);
Would appreciate some help
I guess that you want element-wise division in nowT, like this:
nowT=(4.9130+(0.1173+T.*T.*1.65e-8)./ ...
(lambda1.*lambda1-(0.212+T.*T.*2.7e-8).^2)-lambda1.*lambda1.*2.78e-2);
The change is simply ...1.65e-8)./(lambda1... instead of ...1.65e-8)/(lambda1...
That code gives the following figure in Octave Online.
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.
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 make symbolic functions theta1(t), theta2(t), theta3(t),...,thetaN(t) where N is some parameter I can define in MATLAB. I know that I can use something like sym('theta',[1 N]) to get [theta1, theta2, theta3,..., thetaN]. However, how can I do the same thing with theta being a function of t? The way to hard-code it would be like syms theta1(t) theta2(t) theta3(t) ... thetaN(t), but I want to make this general.
I do not want to directly use the sym command here because "support of character vectors that are not valid variable names and do not define a number will be removed in a future release", meaning something like sym('theta1(t)') would not be valid in future releases.
Any suggestions?
Figured part of it out. I could do something like the following
for i = 1:N
syms(strcat('theta',num2str(i),'(t)'))
end
However, if I want to assign a variable that contains all the symbolic expressions I'm still stuck. If I try
for i = 1:N
my_array(i) = syms(strcat('theta',num2str(i),'(t)'))
end
I get Error using syms (line 133). Using input and output arguments simultaneously is not supported. It works if I use sym instead of syms, but this leads to the warning I mentioned in my original post.
How do I easiest solve an equation=0 with a function as a parameter?
My function with one input variable is called potd(angle), with one output variable, potNRGderiv. I tried:
syms x
solve(potd(x))
This gave me error: Undefined function 'sind' for input arguments of type 'sym'.
Have you got any ideas? Thanks in advance.
solve is the wrong avenue here, unless your function can be rewritten as a simple equation. solve uses muPAD functions which is why you can do solve(sin(x)) but not solve(sind(x)). You can, of course, just do the conversion yourself.
If your function is more complicated or you'd rather not rewrite it, look into fsolve:
x = fsolve(#myfun,x0)
Where x0 is your initial guess - i.e. myfun(x0) is close to 0 - and myfun is a function which takes x and returns a single output. Depending on what your function does, you may have to adjust the options using optimoptions (tolerance, step size, etc) to get a good result.