why am i getting this message: "Array indices must be positive integers or logical values."?

clc
close all 
clear all

abs_val = 978741.3548; %absolute value for the base station
ic = 0.1008; %instrument constant

df = xlsread('data_sheet.xlsx');
values = df(:,9);
dtime = df(:,11);

dr_rate = (values(19)-values(1))/(dtime(19)-dtime(1)); %drift rate
c = dr_rate * dtime;  %correction
x = values - c;  %drift corrected value
del_g = (values(1) - x) * ic;
ab_val = abs_val + del_g;

deg = df(:,1);
min = df(:,2);
sec = df(:,3);

% latitude in radian
lat_rad = (deg + (min/60) + (sec/3600))*(22/7)/180;
gt  = 978031.846*(1 + 0.005278895*(sin(lat_rad)).^2 + 0.000023462*(sin(lat_rad)).^4);  %theoretical value of g 

%latitude correction
del_s = (lat_rad(1) - lat_rad)*(180/(22/7))*111;
lat_corr = 0.811*sin(2*lat_rad).*del_s;

%free air correction
elevation = df(:,7);
fa_corr = 0.3086 * elevation;

%bouguer correction
b_corr = 0.112 * elevation;

%bouguer anomaly
ba = ab_val - gt + lat_corr + fa_corr - b_corr;

%free air anomaly
fa_a = ab_val - gt + lat_corr + fa_corr;

%plotting the contour plot
lat_deg = deg + (min/60) + (sec/3600);

%logitudinal 
lon_deg = df(:,4);
lon_min = df(:,5);
lon_sec = df(:,6);

long_deg = lon_deg + lon_min/60 + lon_sec/3600;

%bouguer anomaly
x1 = linspace(min(long_deg),max(long_deg),10);
y1 = linspace(min(lat_deg),max(lat_deg),10);

[X1,Y1] = meshgrid(x1,y1);

Z1 = griddata(long_deg,lat_deg,ba,X1,Y1,'v4');
[c,h] = contour(x1.y1,Z1)
clabel(c,h)
colorbar()

%free air anomaly

y2 = linspace(min(lat_deg),max(lat_deg),20);
x2 = linspace(min(long_deg),max(long_deg),20);

[X2,Y2] = meshgrid(x2,y2);

Z2 = griddata(long_deg,lat_deg,fa_a,X2,Y2,'v4');
contourf(Z2)
colorbar()




Error in gravity (line 54)
x1 = linspace(min(long_deg),max(long_deg),10);

Answer 1

[Voss]

min = df(:,2);

That line makes min a variable. Then when you try to take min(long_deg) on the error line, MATLAB interprets that as indexing the variable min with the index long_deg instead of using the min() function.

Avoid naming variables with the same names as functions to prevent this problem. Change the variable min to some other name.

[Arpita]

thank you so much. have a lovely day.

Answer 2

[Walter Roberson]

deg = df(:,1);
min = df(:,2);
sec = df(:,3);

min is now a variable not a function. "minutes" and "minimum" same abbreviation.

[Arpita]

thank you so much. have a lovely day.

Answer 3

[Image Analyst]

See the FAQ:

https://matlab.fandom.com/wiki/FAQ#%22Subscript_indices_must_either_be_real_positive_integers_or_logicals.%22