Error: "Invalid first data argument" (when attempting to plot)

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Kevin Steerman
Kevin Steerman 2016-2-16
评论： KSSV 2016-2-16
I am trying to create a scatter plot of: z = ( sin(xy) )2 , where x and y are both independent variables and each point is shown as a square with a defined color (based on it's value). Whenever I attempt to run the code I get the "Invalid first argument" error and it directs me to line 14: (plot(x,y,'s','c')). I honestly have no idea what this means. I have been using MATLAB for only a few months now so practically everything is still pretty new to me. Also, I am supposed to use a for loop to plot each point one-by-one.
if true
x = -3:0.1:3;
y = -3:0.1:3;
z = (sin(x.*y)).^2;
for i = 1:length(z)
if z(i) < 0.1
plot(x,y,'s','b');
elseif z(i) > 0.1 && z(i) < 0.5
plot(x,y,'s','c')
elseif z(i) > 0.5 && z(i) < 0.75
plot(x,y,'s','g')
elseif z(i) > 0.75 && z(i) < 0.95
plot(x,y,'s','r')
else
plot(x,y,'s','b')
end
end
end

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采纳的回答

KSSV
KSSV 2016-2-16
Hello what is 's' in the plot command? 's' has no meaning in plot. You have to follow as below.
if true
x = -3:0.1:3;
y = -3:0.1:3;
z = (sin(x.*y)).^2;
for i = 1:length(z)
if z(i) < 0.1
plot(x,y,'.b');
elseif z(i) > 0.1 && z(i) < 0.5
plot(x,y,'.c')
elseif z(i) > 0.5 && z(i) < 0.75
plot(x,y,'.g')
elseif z(i) > 0.75 && z(i) < 0.95
plot(x,y,'.r')
else
plot(x,y,'.b')
end
end
end
  2 个评论
Kevin Steerman
Kevin Steerman 2016-2-16
When I used the "help plot" function, it said that 'S' would creat square data points. And by looking at the edited code you posted, since my x and y values are multi-column vectors, by using the 'b' (as I did) it was trying to do the integer procedure because I did not specify my x and y datas are vectors. Is that statement correct?
Also, thank you so much for your response!

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