having a problem with my "new love", matlab: I wrote a function to calculate an integral using the trapz-method: `
function [L]=bogenlaenge_innen(schwingungen)
R = 1500; %Ablegeradius
OA = 1; %Amplitude
S = schwingungen; %Schwingungszahl
B = 3.175; %Tapebreite
phi = 0:2.*pi./10000:2.*pi;
BL = sqrt((R-B).^2+2.*(R-B).*OA.*sin(S.*phi)+OA.^2.*(sin(S.*phi)).^2+OA.^2.*S.^2.*(cos(S.*phi)).^2);
L = trapz(phi,BL)`
this works fine when i start it with one specific number out of the command-window. Now I want to plot the values of "L" for several S.
I did the following in a new *.m-file:
W = (0:1:1500);
T = bogenlaenge_innen(W);
plot(W,T)
And there it is:
Error using .*
Matrix dimensions must agree.
What is wrong? Is it just a dot somewhere? I am using matlab for the second day now, so please be patient.... ;) Thank you so much in advance!
PS: just ignore the german part of the code, it does not really matter :)
In your code, the arrays S and phi in the expression sin(S.*phi) should have same size or one of them should be a constant in order the code works
The error is most likely because you have made it so that the number of elements in schwingungen, i.e. W in your code, must be equal to the number of elements in phi. Since size(W) gives you a different result from size(0:2.*pi./10000:2.*pi), you get the error.
The way .* works is that is multiplies each corresponding elements of two matrices provided that they either have the same dimensions or that one of them is a scalar. So your code will work when schwingungen is a scalar, but not when it's a vector as chances are it has a different number of elements from the way you hard coded phi.
The simplest course of action (not necessarily the most Matlabesque though) for you is to loop through the different values of S:
W = (0:1:1500);
T = zeros(size(W); %Preallocate for speed)
for ii = 1:length(W)
T(ii) = bogenlaenge_innen(W(ii));
end
plot(W,T)
In your function you define phi as a vector of 10001 elements.
In this same function you do S.*phi, so if S is not the same length as phi, you will get the "dimensions must agree" error.
In your call to the function you are doing it with a vector of length 1501, so there is your error.
Regards
Related
i am solving a mathematical problem and i can't continue do to the error.
I tried all constant with sin^2(x) yet its the same.
clear
clc
t = 1:0.5:10;
theta = linspace(0,pi,19);
x = 2*sin(theta)
y = sin^2*(theta)*(t/4)
Error using sin
Not enough input arguments.
Error in lab2t114 (line 9)
y = sin^2*(theta)*(t/4)
sin is a function so it should be called as sin(value) which in this case is sin(theta) It may help to consider writing everything in intermediate steps:
temp = sin(theta);
y = temp.^2 ...
Once this is done you can always insert lines from previous calculations into the next line, inserting parentheses to ensure order of operations doesn't mess things up. Note in this case you don't really need the parentheses.
y = (sin(theta)).^2;
Finally, Matlab has matrix wise and element wise operations. The element wise operations start with a period '.' In Matlab you can look at, for example, help .* (element wise multiplication) and help * matrix wise calculation. For a scalar, like 2 in your example, this distinction doesn't matter. However for calculating y you need element-wise operations since theta and t are vectors (and in this case you are not looking to do matrix multiplication - I think ...)
t = 1:0.5:10;
theta = linspace(0,pi,19);
x = 2*sin(theta) %times scalar so no .* needed
sin_theta = sin(theta);
sin_theta_squared = sin_theta.^2; %element wise squaring needed since sin_theta is a vector
t_4 = t/4; %divide by scalar, this doesn't need a period
y = sin_theta_squared.*t_4; %element wise multiplication since both variables are arrays
OR
y = sin(theta).^2.*(t/4);
Also note these intermediate variables are largely for learning purposes. It is best not to write actual code like this since, in this case, the last line is a lot cleaner.
EDIT: Brief note, if you fix the sin(theta) error but not the .^ or .* errors, you would get some error like "Error using * Inner matrix dimensions must agree." - this is generally an indication that you forgot to use the element-wise operators
Can you please tell me what's wrong with the following code?
function [n]=calculate_n(p,delta)
e = 1.6*power(10,-19);
k = 1.38*power(10,-23);
T = 298;
co = 3.25*power(10,13)*e*power(10,4);
er=12.5;
eo=1.0;
Nv=3*power(10,13);
us = log((p*e)/sqrt(2*k*T*er*eo*Nv))*2*k*T;
tmp = delta+(e*e*p)/co+us;
n = 1/(exp((tmp))+1);
end
I am getting matrix dimension error while calculating n. Please help me.
Caller:
e = 1.6*power(10,-19);
x = logspace(13,18);
y=calculate_n(x,0.2*e);
semilogx(x,y,'-s');
grid on;
Just replace n = 1/(exp((tmp))+1); with n = 1./(exp(tmp)+1);. But beware, tmp is so small for these values that exp(tmp) will always be 1. Also, there is a surplus bracket around tmp, you might want to check if you put them correctly.
Edit:
The reason is that A/B tries to solve the system of linear equations A*x = B for x which is not what you wanted. It threw an error because it requires both variables to have the same number of columns. A./B performs element-wise matrix division which is what you wanted. However, if A and B are singular A/B = A./B. See the documentation for more info.
Can anybody help me with this assignment please?
I am new to matlab, and passing this year depends on this assignment, i don't have much time to explore matlab and i already wasted alot of time trying to do this assignment in my way.
I have already wrote the equations on the paper, but transfering the equations into matlab codes is really hard for me.
All i have for now is:
syms h
l = (0.75-h.^2)/(3*sqrt((5*h.^2)/4)); %h is h_max
V_default = (h.^2/2)*l;
dv = diff(V_default); %it's max. when the derivative is max.
h1 = solve( dv ==0);
h_max = (h1>0);
l_max = (0.75-h_max.^2)/(3*sqrt((h_max/2).^2+(h_max.^2)));
V_max = ((h_max.^2)./(2.*l_max));
but it keep give me error "Error using ./
Matrix dimensions must agree.
Error in triangle (line 9)
V_max = ((h_max.^2)./(2.*l_max)); "
Not really helping with the assignment here, but with the Matlab syntax. In the following line:
l_max = (0.75-h_max.^2)/(3*sqrt((h_max/2).^2+(h_max.^2)));
you're using / that is a matrix divide. You might want to use ./ which will divide the terms element by element. If I do this
l_max = (0.75-h_max.^2) ./ (3*sqrt((h_max/2).^2+(h_max.^2)));
then your code doesn't return any error. But I have no idea if it's the correct solution of your assignment, I'll leave that to you!
In line 5, the result h1 is a vector of two values but the variable itself remains symbolic, from the Symbolic Math Toolbox. MATLAB treats such variables slightly different. For that reason, the line h_max = (h1>0) doesn't really do what you expect. As I think from this point, you are interested in one value h_max, I would convert h1 to a regular MATLAB variable and change your code to the following:
h1 = double(solve( dv ==0)); % converts symbolic to regular vectors
h_max = h1(h1>0); % filters out all negative and zero values
l_max = (0.75-h_max.^2)/(3*sqrt((h_max/2).^2+(h_max.^2)));
V_max = ((h_max.^2)./(2.*l_max));
EDIT.
If you still have error, it means solve( ...) returns more than 1 positive values. In this case, as suggested, use dotted operations, such as ./ but the results in l_max and V_max will not be a single value but vectors of the same size as h_max. Which means you don't have one max Volume.
My teacher has given me a task of expressing a sound file(.wav) in polynomial form in MATLAB(curve fitting),.
I tried using polyfit() like this:-
a=wavread('filename');
x=linspace(0,1,239915);
p=polyfit(x,a,4);
display(p);
but I am getting error as
X and Y vectors must be the same size
Please help me.
Size of a is not 239915, it is for x we have taken these many samples, for line space, by the way, why do we need x for polyfit().
Thank you in advanced
Try this
a = wavread('filename')
x = linspace(0, 1, numel(a))';
p = polyfit(x,a,4);
display(p)
Note that I transpose linspace output as it returns a row vector where wavread returns a column vector, which is why you get the error message.
So I'm just trying to plot 4 different subplots with variations of the increments. So first would be dx=5, then dx=1, dx=0.1 and dx=0.01 from 0<=x<=20.
I tried to this:
%for dx = 5
x = 0:5:20;
fx = 2*pi*x *sin(x^2)
plot(x,fx)
however I get the error inner matrix elements must agree. Then I tried to do this,
x = 0:5:20
fx = (2*pi).*x.*sin(x.^2)
plot(x,fx)
I get a figure, but I'm not entirely sure if this would be the same as what I am trying to do initially. Is this correct?
The initial error arose since two vectors with the same shape cannot be squared (x^2) nor multiplied (x * sin(x^2)). The addition of the . before the * and ^ operators is correct here since that will perform the operation on the individual elements of the vectors. So yes, this is correct.
Also, bit of a more advanced feature, you can use an anonymous function to aid in the expressions:
fx = #(x) 2*pi.*x.*sin(x.^2); % function of x
x = 0:5:20;
plot(x,fx(x));
hold('on');
x = 0:1:20;
plot(x,fx(x));
hold('off');