Queries on the use of "double"

1 次查看（过去 30 天）
Doc Ed
Doc Ed 2020-9-17
评论： Ameer Hamza 2020-9-30
Hi MATLAB, during our laboratory simulation, when we evaluate sin(x) when x=2, and use the "subs" command, some students reported the answer as sin(2) instead of 0.9093. How come? But when they use the "double" command, they arrived 0.9093. But other computers don;t need double command.
Case 1:
Script:
y=input('Input f(x): ');
x=input('Input x for f(x): ');
val=subs(y,x)
Result:
Input f(x): sin(x)
Input x for f(x): 2
val=
sin(2)
Case 2:
Script:
y=input('Input f(x): ');
x=input('Input x for f(x): ');
val=subs(y,x)
Result:
Input f(x): sin(x)
Input x for f(x): 2
val=
0.9093
Why did some computers reported sin(2) instead of 0.9093 with the same script? Why do some programs need double command but other computeres don't? Thank you

请先登录，再回答此问题。

采纳的回答

Ameer Hamza
Ameer Hamza 2020-9-17
This is probably caused by symbolic preferences on your machines. I guess you have defined x as a symbolic variable before this code.
syms x
By default, in the case of symbolic variables, MATLAB does not convert to a floating-point value; therefore, sin(2) is the default answer. If you are getting a value of 0.9093, then that means that somehow the preference has been changed by running
sympref("FloatingPointOutput", 1)
If you want always to get floating-point output, run the above line on all machines. To get the default preferences, run
sympref("default")

更多回答（1 个）

BOB MATHEW SYJI
BOB MATHEW SYJI 2020-9-17
I think the first one uses syms command anywhere in the script while the second one does not. While you use syms command the entire expression is given as output. So you have to manually give double(output) to get the value.

类别

在 Help Center 和 File Exchange 中查找有关 Common Operations 的更多信息

标签

Community Treasure Hunt

Find the treasures in MATLAB Central and discover how the community can help you!

Start Hunting!

Translated by