why If statement is not work?

2018 11 22
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更新时间：2018 11 22
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eq1 have at each nf the values 0.186170065500000 0.336133515500000 0.486096965500000 0.636060415500000 0.786023865500000 0.935987315500000 1.08595076550000
i want to plot out1 when eq1 >1so, out1 should be calculated at 1.08595076550000
eq1=((bwf*nf)./wi)+((bwm*nm1)./wi);
out1=(bwf*nf)./wi;
plot (eq1);
hold on
if all(eq1 >=1)
out1=(bwf*nf)./wi;
plot (out1);
end

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Adam
Adam 2018-11-22
To answer the question in the title, read the logic of your if statement.
if all( eq1 >= 1 )
i.e. it will only evaluate to true if all the values in eq1 are greater than or equal to 1. The result is a scalar logical, as needed generally for an if statement, but it isn't capturing what you want.

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madhan ravi
madhan ravi 2018-11-22
编辑：madhan ravi 2018-11-22

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maryhan mohamed
maryhan mohamed 2018-11-22
it works now
but,
nf 1:7
so eq1 will be >1 at nf=7 only
when out1 is calculated by the above code it calculate all nf 1:7 not nf=7
madhan ravi
madhan ravi 2018-11-22
Did you read the first link?
maryhan mohamed
maryhan mohamed 2018-11-22
编辑：madhan ravi 2018-11-22
yes, i got my floating point problem
but
nf = 1, 2,3,4,5,6,7
and
eq1 will be >1 at nf=7
please, i want to calculate the out1 when eq1 >1 at nf =7
out1=(bwf*nf)./wi;
my code give me result for out1 at each nf not at nf =7
eq1=((bwf*nf)./wi)+((bwm*nm1)./wi);
out1=(bwf*nf)./wi;
plot (eq1);
hold on
if sum(eq1)>=1
out1=(bwf*nf)/wi;
plot (out1);
end
madhan ravi
madhan ravi 2018-11-22
if abs(eq1-1)>1e-4 %set tolerance by the way you didn't read the links I suggested
maryhan mohamed
maryhan mohamed 2018-11-22
from the shown code,
eq1=((bwf*nf)./wi)+((bwm*nm1)./wi);
out1=(bwf*nf)./wi;
plot (eq1);
hold on
if abs(eq1-1)>1e-4
out1=(bwf*nf)/wi;
plot (out1);
end
the output will be
eq1=0.186170065500000 0.336133515500000 0.486096965500000 0.636060415500000 0.786023865500000 0.935987315500000 1.08595076550000
out1=0.149963450000000 0.299926900000000 0.449890350000000 0.599853800000000 0.749817250000000 0.899780700000000 1.04974415000000
please,, what i want is to make out1 result = 1.04974415000000 only % nf=7 at eq1=1.08595076550000 which is greater than 1.
thanks for ur helping,
maryhan mohamed
maryhan mohamed 2018-11-22
wi=10000000;
nf=1:7;
nm1=1;
bwf=1499634.50;
bwm=362066.155;
madhan ravi
madhan ravi 2018-11-22
编辑：madhan ravi 2018-11-22
wi=10000000;
nf=1:7;
nm1=1;
bwf=1499634.50;
bwm=362066.155;
eq1=[0.186170065500000 0.336133515500000 0.486096965500000 0.636060415500000 0.786023865500000 0.935987315500000 1.08595076550000];
idx=abs(eq1-0)>1
result=(bwf*nf)/wi;
result=result(idx)

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Image Analyst
Image Analyst 2018-11-22

3 个投票

The link about comparing equality of floating point numbers is good information, though it doesn't apply here since none of your eq1 numbers are expected to be exactly 1 - they're all clearly either more than or less than 1.
Your original code
wi=10000000;
nf=1:7;
nm1=1;
bwf=1499634.50;
bwm=362066.155;
eq1=((bwf*nf)./wi)+((bwm*nm1)./wi);
out1=(bwf*nf)./wi;
plot (eq1);
hold on
if all(eq1 >=1)
out1=(bwf*nf)./wi;
plot (out1);
end
did plot the first plot. It did not plot the second plot since not ALL elements of eq1 were more than 1. I believe you want masking, where you plot only those elements where eq1 > 1 and no others ("i want to plot out1 when eq1 >1"). To do that, see this corrected code:
wi=10000000;
nf=1:7;
nm1=1;
bwf=1499634.50;
bwm=362066.155;
eq1=((bwf*nf)./wi)+((bwm*nm1)./wi)
% Plot eq1.
plot (eq1, 'bo-');
xlabel('index', 'FontSize', 15);
ylabel('eq1', 'FontSize', 15);
grid on;
% Compute out1.
out1 = (bwf * nf) ./ wi % Note: same as
% Create a mask where only those where eq1 > 1 are true.
mask = eq1 > 1
% Plot only those where eq1 > 1 (where the mask is true).
hold on;
x = 1 : length(out1)
plot (x(mask), out1(mask), 'r*', 'MarkerSize',13, 'LineWidth', 2);
legend('eq1', 'out1', 'Location', 'north');
0000 Screenshot.png
Your original eq1 (outside the if block) is plotted in blue while the points of out1, only where eq1 is greater than 1, are plotted in red.

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