Issue with fprintf in a loop
显示 更早的评论
Here is my code :
close all; clear all; clc
g = 1.4; % Specific heat ratio for air
beta = 0:pi/1800:pi/2; % Range for shock wave angle in rad
m = 0;
% theta
for M1 = 1:0.5:10 % Upstream Mach Number from 1 to 10
m = m+1;
p(m)=fprintf('%.2n' , M1);
% theta-beta-M relation
A = ((M1^2)*((sin(beta)).^2))-1;
B = ((g+(cos(2*beta)))*M1^2)+2;
theta = atan(2*cot(beta).*A./B);
% max. theta for a M1
maxtheta(m) = max(theta); % max theta for the Mach No.
maxbeta(m) = beta(theta==maxtheta(m)); % find the beta for max. theta
plot(theta*180/pi,beta*180/pi,'-b')
if M1<=5
x(m)=(theta(beta==60*pi/180)*180/pi);
if x(m)>0
txt= sprintf('M1=%d',p(m));
text(x(m),60,txt)
end
end
hold on
end
plot(maxtheta*180/pi,maxbeta*180/pi,'-r','Linewidth',1.5)
xlabel('\theta')
ylabel('\beta')
axis([0 50 0 90])
When i don't use the fprintf function, the M1 displayed on the graph have many zeros. SO i am trying to get rid of those useless zeros with fprintf. However when I use Fprintf in my loop it only returns 4 and not 1.0 ; 1.5 ; 2.0 and so on.
Could someone help me on that ?
Thank you
采纳的回答
fprintf returns the number of bytes written. It's always zero in this case because '%.2n' is not a valid format.
Instead, use sprintf to construct txt, and use an appropriate format.
close all; clear all; clc
g = 1.4; % Specific heat ratio for air
beta = 0:pi/1800:pi/2; % Range for shock wave angle in rad
m = 0;
% theta
for M1 = 1:0.5:10 % Upstream Mach Number from 1 to 10
m = m+1;
% theta-beta-M relation
A = ((M1^2)*((sin(beta)).^2))-1;
B = ((g+(cos(2*beta)))*M1^2)+2;
theta = atan(2*cot(beta).*A./B);
% max. theta for a M1
maxtheta(m) = max(theta); % max theta for the Mach No.
maxbeta(m) = beta(theta==maxtheta(m)); % find the beta for max. theta
plot(theta*180/pi,beta*180/pi,'-b')
if M1<=5
x(m)=(theta(beta==60*pi/180)*180/pi);
if x(m)>0
txt= sprintf('M1=%.1f',M1);
text(x(m),60,txt)
end
end
hold on
end
plot(maxtheta*180/pi,maxbeta*180/pi,'-r','Linewidth',1.5)
xlabel('\theta')
ylabel('\beta')
axis([0 50 0 90])
6 个评论
Adrien
2023-10-19
%.1f is fixed-point with one digit after the decimal point.
%.99g is 99 significant digits with no trailing zeros.
sprintf('%.1f',1.1)
sprintf('%.99g',1.1)
Voss
2023-10-19
You're welcome! Any questions, let me know. Otherwise, please "Accept" this answer. Thanks!
%.99g is a quick shorthand that people sometimes use to mean "all of the decimal places in the number". But for that purpose it fails for some of the smaller numbers, which is why I tend to use %.999g myself.
The actual maximum number of decimal places needed is
E = eps(0);
Ed = sprintf('%.9999f', E)
Ed = regexprep(Ed, '0+$', '');
L = length(Ed) - 2
fmt = sprintf('%%.%gf', L)
Ed2 = sprintf(fmt, E)
strcmp(Ed, Ed2)
1074 if you use a %f format. If you use a %g format the maximum needed is 754.
"But whats the difference between %.1f and %.99g ? (Showed on the post below)"
For your use-case %.9g would likely be better. Compare:
V = [1,1.1,1.9876];
fprintf('%.1f\n',V) % fixed-point, one fractional digit
fprintf('%.9g\n',V) % nine significant figures, no trailing zeros
更多回答（0 个）
类别
在 帮助中心 和 File Exchange 中查找有关 Logical 的更多信息
Translated by 
