Matlab isn't ploting the function
显示 更早的评论
Hi everyone!
I'm trying to get Matlab to fetch the values of an excel cell in a particular sheet in a particular workbook, then computing a piecewise function and then presenting the results in a logarithmic scale. All fine and cool but then, when the graph shows up, nothing is on it.
I'm very very new to Matlab (like two days new) and i've been strugling with it. Any help?
eta_l = xlsread('calculos.xlsx','Theoretical Predictions','S2');
eta_0 = xlsread('calculos.xlsx','Theoretical Predictions','S2');
l_c = xlsread('calculos.xlsx','Theoretical Predictions','P3');
sigma_f = xlsread('calculos.xlsx','Base Values','B3');
v_f = xlsread('calculos.xlsx','Burn','E23');
E_m = xlsread('calculos.xlsx','Base Values','D2');
E_f = xlsread('calculos.xlsx','Base Values','B2');
d = xlsread('calculos.xlsx','Base Values','B5');
for x=logspace(-6,2)
if x < l_c
y1=((eta_l.*eta_0.*((v_f.*sigma_f.*E_m)./(E_f.*d.*sqrt(3))).*x)+((sigma_f.*E_m.*(1-v_f))./E_f));
else
y2=(eta_l.*eta_0.*(((-sigma_f.*v_f.*l_c)./2).*(1./x)+(sigma_f.*v_f)))+(((sigma_f.*E_m)./E_f).*(1-v_f));
end
end
semilogx(x,y1,x,y2);
grid on
Thanks in advance!
P.S.:
The function is as follows if you're having trouble reading it from the code
where "l" is "x".
3 个评论
Mathieu NOE
2021-7-13
hello
are you sure that x, y1 and y2 exist ? and are not NaN ?
what do you get in your workspace when you type whos ?
João Novais
2021-7-13
Yes they do exist. For instance this is the graph of the whole function y2 by it's own
The thing is that i'm having trouble ploting them together. When i type "whos" it appears that all my variables appear as "double"
Name Size Bytes Class Attributes
E_f 1x1 8 double
E_m 1x1 8 double
d 1x1 8 double
eta_0 1x1 8 double
eta_l 1x1 8 double
l_c 1x1 8 double
sigma_f 1x1 8 double
v_f 1x1 8 double
x 1x1 8 double
y 1x100 800 double
y1 1x1 8 double
y2 1x1 8 double
Mathieu NOE
2021-7-13
there is something wrong probably in this for loop
for x=logspace(-6,2)
if x < l_c
y1=((eta_l.*eta_0.*((v_f.*sigma_f.*E_m)./(E_f.*d.*sqrt(3))).*x)+((sigma_f.*E_m.*(1-v_f))./E_f));
else
y2=(eta_l.*eta_0.*(((-sigma_f.*v_f.*l_c)./2).*(1./x)+(sigma_f.*v_f)))+(((sigma_f.*E_m)./E_f).*(1-v_f));
end
end
at the end , x, y1 and y2 are scalars (see dimensions displayed in your workspace) and not vectors (should be same size as y ? )
the for loop must be rewritten with indexes for x and y1 , y2 - not the way you do it
suggestion (I cannot test it without your data and I am not sure that initializing y1 and y2 with zeros is appropriate - you should double check that) :
N = 100;
x =logspace(-6,2,N) ;
y1 = zeros(1,N);
y2 = zeros(1,N);
for ci = 1:N
if x(ci) < l_c
y1(ci)=((eta_l.*eta_0.*((v_f.*sigma_f.*E_m)./(E_f.*d.*sqrt(3))).*x(ci))+((sigma_f.*E_m.*(1-v_f))./E_f));
else
y2(ci)=(eta_l.*eta_0.*(((-sigma_f.*v_f.*l_c)./2).*(1./x(ci))+(sigma_f.*v_f)))+(((sigma_f.*E_m)./E_f).*(1-v_f));
end
end
采纳的回答
I do not have any of the data, however I believe that I understand the problem:
for x=logspace(-6,2)
y = x.^2;
end
figure
plot(x, y, '.-')
However this produces a different result:
x=logspace(-6,2)
y = x.^2;
figure
plot(x, y, '.-')
% return
Try something like this —
x=logspace(-6,2)
idx = x < l_c
y1=((eta_l.*eta_0.*((v_f.*sigma_f.*E_m)./(E_f.*d.*sqrt(3))).*x(idx))+((sigma_f.*E_m.*(1-v_f))./E_f));
y2=(eta_l.*eta_0.*(((-sigma_f.*v_f.*l_c)./2).*(1./x(~idx))+(sigma_f.*v_f)))+(((sigma_f.*E_m)./E_f).*(1-v_f));
Be sure that all the ‘x’ references are ‘x(idx)’ or ‘x(~idx)’. I only found one in each assignment, and changed those.
.
4 个评论
João Novais
2021-7-13
Star Strider
2021-7-13
The ‘x’ vectors need to change as well:
x=logspace(-6,2);
idx = x < l_c;
y1=((eta_l.*eta_0.*((v_f.*sigma_f.*E_m)./(E_f.*d.*sqrt(3))).*x(idx))+((sigma_f.*E_m.*(1-v_f))./E_f));
y2=(eta_l.*eta_0.*(((-sigma_f.*v_f.*l_c)./2).*(1./x(~idx))+(sigma_f.*v_f)))+(((sigma_f.*E_m)./E_f).*(1-v_f));
plot(x(idx),y1,x(~idx),y2)
That should work.
.
João Novais
2021-7-14
Star Strider
2021-7-14
As always, my pleasure!
.
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