清空筛选条件
清空筛选条件

How to find when the value is 0 in an array?

119 次查看（过去 30 天）
Adam Luckman
Adam Luckman 2018-12-5
评论： Walter Roberson 2022-8-8
Im plotting a graph of X against Y and i want to know the value of X when Y = 0. I have tried to use the find command and doing find(Y==0) but because in the array there is no exact zero number (goes to 0.00024 then to negative) it wont return anything.
Y = (U_y .* time) - (0.5 .* g .* (time).^2) + handles.Height;
Index = find(Y==0)
X_point = X(Index)

请先登录，再回答此问题。

回答（2 个）

Rik
Rik 2018-12-5
This answer contains code to find the zero crossing in a vector
https://www.mathworks.com/matlabcentral/answers/267222-easy-way-of-finding-zero-crossing-of-a-function#answer_209072
Walter Roberson
Walter Roberson 2018-12-5
[~, Index] = min(abs(Y));
The zero crossing will be between the point at Index and the next point over in one of the two directions.
You could also use
mask = Y > 0;
% goes from positive to negative ?
Index = find(Y(1:end-1) & ~Y(2:end));
if isempty(Index);
% goes from negative to positive ?
Index = find(~Y(1:end-1) & Y(2:end));
end
if isempty(Index)
%no zero crossing
end
  2 个评论
Greg Simmons
Greg Simmons 2022-8-8
very clever!... this second script helped me a lot. Thanks Walter.
Walter Roberson
Walter Roberson 2022-8-8
The script should probably be
mask = Y > 0;
% goes from positive to negative ?
Index = find(mask(1:end-1) & ~mask(2:end));
if isempty(Index);
% goes from negative to positive ?
Index = find(~mask(1:end-1) & mask(2:end));
end
if isempty(Index)
%no zero crossing
end

请先登录，再进行评论。

类别

在 Help Center 和 File Exchange 中查找有关 Matrices and Arrays 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