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Matlab should have give array but it gives a number. How to fix?

Asked by Ege Tunç on 16 Mar 2019 at 19:14
Latest activity Edited by Jan
on 18 Mar 2019 at 7:20
Accepted Answer by Jan
I have a code to calculate some lambda values then uses these values with our r values to find d values. However, these values are 1x21 array but the given answer is just a number why? and how to fix this?
U=[10 9.7 9.4 9.1 8.8 8.5 8.2 7.9 7.6 7.3 7.0 6.7 6.4 6.1 5.8 5.5 5.2 4.9 4.6 4.3 4.0];
h=6.625.*10.^(-34);
m=9.109.*10.^(-31);
e=1.602.*10.^(-19);
lambda=h./sqrt(2.*m.*e.*U.*1000);
R=65.*10.^(-3);
r1i=[0.7 0.75 0.8 0.85 0.9 0.9 1.05 1.05 1.1 1.1 1.1 1.15 1.15 1.10 1.10 1.10 1.10 1.15 1.10 1.15 1.2];
r1o=[1.2 1.3 1.35 1.4 1.4 1.45 1.5 1.55 1.55 1.6 1.6 1.67 1.67 1.75 1.75 1.8 1.9 1.9 2 2.05 2.1];
r2i=[0.75 0.75 0.85 0.95 1 1 1.05 1.1 1.1 1.1 1.1 1.15 1.2 1.2 1.25 1.25 1.25 1.3 1.3 1.3 1.35];
r2o=[1.25 1.3 1.4 1.4 1.45 1.45 1.5 1.55 1.6 1.65 1.65 1.7 1.7 1.75 1.85 1.9 1.9 1.95 2 2.05 2.1];
r3i=[0.7 0.75 0.75 0.8 0.85 0.85 0.9 0.95 1 1 1 1 1.05 1.05 1.05 1.1 1.1 1.15 1.15 1.15 1.2];
r3o=[1.2 1.25 1.3 1.35 1.4 1.45 1.5 1.5 1.55 1.6 1.6 1.65 1.7 1.7 1.75 1.8 1.85 1.9 1.95 2 2.05];
d1i=(2*R.*lambda)/(10.^(-2).*r1i);
d1o=(2*R.*lambda)/(10.^(-2).*r1o);
d2i=(2*R.*lambda)/(10.^(-2).*r2i);
d2o=(2*R.*lambda)/(10.^(-2).*r2o);
d3i=(2*R.*lambda)/(10.^(-2).*r3i);
d3o=(2*R.*lambda)/(10.^(-2).*r3o);
dinner=(d1i+d2i+d3i)/3
douter=(d1o+d2o+d3o)/3

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1 Answer

Answer by Jan
on 16 Mar 2019 at 19:23
Edited by Jan
on 18 Mar 2019 at 7:20
 Accepted Answer

Use the elementwise division:
d1i=(2*R.*lambda) ./ (10.^(-2).*r1i);
% ^
You have used the elementwise operations exhaustively, even if they are not needed, because the operands are scalars only. But at the only location, where it is needed, the matrix division / is applied. I'd use:
d1i = 2 * R * lambda ./ (1e-2 * r1i);
% or even nicer:
d1i = 200 * R * lambda ./ r1i;
By the way, compare
h=6.625.*10.^(-34);
with
h = 6.625e-34;
The first is an expensive power operation, while the second is a cheap constant - and nicer. Then your code becomes:
U = [10 9.7 9.4 9.1 8.8 8.5 8.2 7.9 7.6 7.3 7.0 6.7 6.4 6.1 5.8 5.5 5.2 4.9 4.6 4.3 4.0];
h = 6.625e-34;
m = 9.109e-31;
e = 1.602e-19;
lambda = h ./ sqrt(2 * m * e * U * 1000);
R = 65e-3;
ri = [0.7 0.75 0.8 0.85 0.9 0.9 1.05 1.05 1.1 1.1 1.1 1.15 1.15 1.10 1.10 1.10 1.10 1.15 1.10 1.15 1.2; ...
0.75 0.75 0.85 0.95 1 1 1.05 1.1 1.1 1.1 1.1 1.15 1.2 1.2 1.25 1.25 1.25 1.3 1.3 1.3 1.35; ...
0.7 0.75 0.75 0.8 0.85 0.85 0.9 0.95 1 1 1 1 1.05 1.05 1.05 1.1 1.1 1.15 1.15 1.15 1.2];
ro = [1.2 1.3 1.35 1.4 1.4 1.45 1.5 1.55 1.55 1.6 1.6 1.67 1.67 1.75 1.75 1.8 1.9 1.9 2 2.05 2.1; ...
1.25 1.3 1.4 1.4 1.45 1.45 1.5 1.55 1.6 1.65 1.65 1.7 1.7 1.75 1.85 1.9 1.9 1.95 2 2.05 2.1; ...
1.2 1.25 1.3 1.35 1.4 1.45 1.5 1.5 1.55 1.6 1.6 1.65 1.7 1.7 1.75 1.8 1.85 1.9 1.95 2 2.05];
di = 200 * R * lambda ./ ri; % Auto-expand, >= R2016b
do = 200 * R * lambda ./ ro; % Auto-expand, >= R2016b
dinner = mean(di, 1)
douter = mean(do, 1)
Less chances for typos.

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later, we found the dot issue, Thanks :)

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