How do I plot 5e^(0.5t)sin(2*pi*t)

조회 수: 4 (최근 30일)
Monqiue Parrish
Monqiue Parrish 2023년 2월 24일
댓글: Les Beckham 2023년 2월 24일
% I have tried to plot 5e^(0.5t)sin(2pi*t) but my graph just show a negative exponential
% But when I compared to demos it's completely wrong
t1 = 0:10;
e = exp((0.5)*t1);
num6 = (5).*e.*sin((2)*pi*t1);
plot(t1, num6, 'c')

채택된 답변

Les Beckham
Les Beckham 2023년 2월 24일
편집: Les Beckham 2023년 2월 24일
t1 = 0:10;
e = exp((0.5)*t1);
num6 = (5).*e.*sin((2)*pi*t1);
plot(t1, num6, 'c')
grid on
You are plotting your exponential term multiplied by the sine of integer multiples of 2*pi which should be zero. Due to floating point precision issues, it is instead very close to zero and increasing in a negative direction. This causes your plot to look the way it does.
t1 = 0:10;
plot(t1, sin(2*pi*t1), '.')
grid on
If you add points that aren't integer multiples of 2*pi you will see the real behavior of your equation.
t1 = 0:0.01:10;
e = exp(0.5 * t1);
num6 = 5 * e .* sin(2*pi*t1);
plot(t1, num6, 'c')
grid on
  댓글 수: 2
Monqiue Parrish
Monqiue Parrish 2023년 2월 24일
Thank you that makes more sense now.
Les Beckham
Les Beckham 2023년 2월 24일
You are quite welcome.

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추가 답변 (2개)

Torsten
Torsten 2023년 2월 24일
이동: Torsten 2023년 2월 24일
Note that sin(2*pi*t) = 0 for t = 0,1,2,3,...,10.
And these are the only points for t you specified.
  댓글 수: 1
Steven Lord
Steven Lord 2023년 2월 24일
You can see this even better if you use sinpi instead of sin.
format longg
t = (0:10).';
y1 = sin(2*pi*t)
y1 = 11×1
1.0e+00 * 0 -2.44929359829471e-16 -4.89858719658941e-16 -7.34788079488412e-16 -9.79717439317883e-16 -1.22464679914735e-15 -1.46957615897682e-15 -1.71450551880629e-15 -1.95943487863577e-15 -2.20436423846524e-15
y2 = sinpi(2*t)
y2 = 11×1
0 0 0 0 0 0 0 0 0 0

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Image Analyst
Image Analyst 2023년 2월 24일
You had so few points that you were subsampling the shape away and couldn't see the oscillations. Use more data points. by using linspace. Try it this way:
t1 = linspace(0, 10, 1000);
e = exp(0.5 * t1);
num6 = 5 .* e .* sin(2 * pi * t1);
plot(t1, num6, 'c-', 'LineWidth', 2);
grid on
xlabel('t1')
ylabel('num6')
title('num6 = 5 .* e .* sin(2 * pi * t1)')

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