addRule throws "Do not use a rule keyword as a variable name."

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Michael on 4 Feb 2026 at 10:45

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Commented: Walter Roberson on 6 Feb 2026 at 22:51

I get the error on line 44 of my code: fis = addRule(fis,all); I've tried changing the name of the variable name (all) to other names, and the fis. I've removed spaces from my variables or renamed them completely.

% Create a Fuzzy Inference System (FIS) with the name "IFR"
fis = mamfis('Name', 'IFR');
% Add a variable "input" to the FIS
fis = addInput(fis, [0 200], 'Name', 'MAP_mm');
% Add membership functions for variable "input"
fis = addMF(fis, "MAP_mm", "trapmf", [0 0 55 75], 'Name',"Low");   
fis = addMF(fis, "MAP_mm", "trapmf", [55 75 100 120], 'Name',"Normal");
fis = addMF(fis, "MAP_mm", "trapmf", [100 120 200 200], 'Name',"High");    
% HOU trapezoidal
fis = addInput(fis, [0 200], 'Name', 'HOU_ml-hr');
% HOU Low trapezoidal
fis = addMF(fis, "HOU_ml-hr", "trapmf", [0 0 30 40], 'Name',"Low");
% HOU Normal trapezoidal
fis = addMF(fis, "HOU_ml-hr", "trapmf", [30 40 100 125], 'Name',"Normal");
% HOU High trapezoidal
fis = addMF(fis, "HOU_ml-hr", "trapmf", [100 125 200 200], 'Name',"High");
% Add output variable to the FIS
fis = addOutput(fis, [0 2000], 'Name', 'IFR_ml-hr');
% Add membership functions for output variable
fis = addMF(fis, "IFR_ml-hr", "trapmf", [0 0 60 100], 'Name',"Low");
fis = addMF(fis, "IFR_ml-hr", "trapmf", [0 100 200 400], 'Name',"Maintain");
fis = addMF(fis, "IFR_ml-hr", "trapmf", [200 400 600 800], 'Name',"Moderate");
fis = addMF(fis, "IFR_ml-hr", "trapmf", [600 800 1000 1500], 'Name',"High");
fis = addMF(fis, "IFR_ml-hr", "trapmf", [1000 1500 2000 2000], 'Name',"Very_High");
% Create Rules for the FIS
r1 = "If HOU_ml-hr == Low & MAP_mm == Low => IFR_ml-hr == Very_High";
r2 = "If HOU_ml-hr == Normal & MAP_mm == Low => IFR_ml-hr == High";
r3 = "If HOU_ml-hr == High & MAP_mm == Low => IFR_ml-hr == Moderate";
r4 = "If HOU_ml-hr == Low & MAP_mm == Normal => IFR_ml-hr == Moderate";
r5 = "If HOU_ml-hr == Low & MAP_mm == High => IFR_ml-hr == Low";
r6 = "If HOU_ml-hr == Normal & MAP_mm == Normal => IFR_ml-hr == Maintain";
r7 = "If HOU_ml-hr == Normal & MAP_mm == High => IFR_ml-hr == Low";
r8 = "If HOU_ml-hr == High & MAP_mm == Normal =>IFR_ml-hr == Maintain";
r9 = "If HOU_ml-hr == High & MAP_mm == High => IFR_ml-hr == Low";
all = [r1 r2 r3 r4 r5 r6 r7 r8 r9];
% Add rules and enable rule viewing/debugging
fis = addRule(fis,all);
Error using FuzzyInferenceSystem/addRule (line 1153)
Do not use a rule keyword as a variable name.
% Evaluate the FIS for inputs [MAP HOU]
sampleInput = [110 120; 60 25; 30 150; 180 90];
out = evalfis(fis, sampleInput);
% Plot membership functions
subplot(3,1,1)
plotmf(fis, 'input', 1)
subplot(3,1,2)
plotmf(fis, 'input', 2)
subplot(3,1,3)
plotmf(fis, 'output',3)

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Answer 1

Walter Roberson on 4 Feb 2026 at 11:29

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Rewriting the rules as words works.

% Create a Fuzzy Inference System (FIS) with the name "IFR"

fis = mamfis('Name', 'IFR');

% Add a variable "input" to the FIS

fis = addInput(fis, [0 200], 'Name', 'MAP_mm');

% Add membership functions for variable "input"

fis = addMF(fis, "MAP_mm", "trapmf", [0 0 55 75], 'Name',"Low");

fis = addMF(fis, "MAP_mm", "trapmf", [55 75 100 120], 'Name',"Normal");

fis = addMF(fis, "MAP_mm", "trapmf", [100 120 200 200], 'Name',"High");

% HOU trapezoidal

fis = addInput(fis, [0 200], 'Name', 'HOU_ml-hr');

% HOU Low trapezoidal

fis = addMF(fis, "HOU_ml-hr", "trapmf", [0 0 30 40], 'Name',"Low");

% HOU Normal trapezoidal

fis = addMF(fis, "HOU_ml-hr", "trapmf", [30 40 100 125], 'Name',"Normal");

% HOU High trapezoidal

fis = addMF(fis, "HOU_ml-hr", "trapmf", [100 125 200 200], 'Name',"High");

% Add output variable to the FIS

fis = addOutput(fis, [0 2000], 'Name', 'IFR_ml-hr');

% Add membership functions for output variable

fis = addMF(fis, "IFR_ml-hr", "trapmf", [0 0 60 100], 'Name',"Low");

fis = addMF(fis, "IFR_ml-hr", "trapmf", [0 100 200 400], 'Name',"Maintain");

fis = addMF(fis, "IFR_ml-hr", "trapmf", [200 400 600 800], 'Name',"Moderate");

fis = addMF(fis, "IFR_ml-hr", "trapmf", [600 800 1000 1500], 'Name',"High");

fis = addMF(fis, "IFR_ml-hr", "trapmf", [1000 1500 2000 2000], 'Name',"Very_High");

% Create Rules for the FIS

r1 = "If HOU_ml-hr is Low and MAP_mm is Low then IFR_ml-hr is Very_High";

r2 = "If HOU_ml-hr is Normal and MAP_mm is Low then IFR_ml-hr is High";

r3 = "If HOU_ml-hr is High and MAP_mm is Low then IFR_ml-hr is Moderate";

r4 = "If HOU_ml-hr is Low and MAP_mm is Normal then IFR_ml-hr is Moderate";

r5 = "If HOU_ml-hr is Low and MAP_mm is High then IFR_ml-hr is Low";

r6 = "If HOU_ml-hr is Normal and MAP_mm is Normal then IFR_ml-hr is Maintain";

r7 = "If HOU_ml-hr is Normal and MAP_mm is High then IFR_ml-hr is Low";

r8 = "If HOU_ml-hr is High and MAP_mm is Normal then IFR_ml-hr is Maintain";

r9 = "If HOU_ml-hr is High and MAP_mm is High then IFR_ml-hr is Low";

all = [r1 r2 r3 r4 r5 r6 r7 r8 r9];

% Add rules and enable rule viewing/debugging

fis = addRule(fis,all);

% Evaluate the FIS for inputs [MAP HOU]

sampleInput = [110 120; 60 25; 30 150; 180 90];

out = evalfis(fis, sampleInput);

% Plot membership functions

subplot(3,1,1)

plotmf(fis, 'input', 1)

subplot(3,1,2)

plotmf(fis, 'input', 2)

subplot(3,1,3)

plotmf(fis, 'output',1)

●

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Michael on 4 Feb 2026 at 22:17

Thanks! I get another error when I run the code now, though i believe it is unrelaed. I get"Access violation - no RTTI data!"

Thank you for the help! I really appreciate it.

Walter Roberson on 5 Feb 2026 at 20:06

There used to be a bug report about that message, https://www.mathworks.com/support/bugreports/1465379?s_tid=answers_rc2-2_p5_MLT that was related to savefig()

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Answer 2

Sam Chak on 5 Feb 2026 at 3:44

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Hi @Michael

If you prefer to use the symbolic approach (==, =>) rather than the linguistic approach (If–Then) as demonstrated by @Walter Roberson, do not use the reserved fuzzy rule-related terms such as "If" and "Then". In your case, when you specified "If HOU_ml-hr == Low", MATLAB interprets this as if you had inadvertently used the phrase "If HOU_ml-hr" as a single variable name. I have made the corrections below, as well as slightly "beautified" the plots to prevent overlapping linguistic names.

If you like the explanation and the enhanced plots, please consider voting 👍 for this Answer.

% Create a Fuzzy Inference System (FIS) with the name "IFR"

fis = mamfis('Name', 'IFR');

% Input variable "MAP"

fis = addInput(fis, [0 200], 'Name', 'MAP_mm');

fis = addMF(fis, "MAP_mm", "trapmf", [ 0 0 55 75], 'Name', "Low");

fis = addMF(fis, "MAP_mm", "trapmf", [ 55 75 100 120], 'Name', "Normal");

fis = addMF(fis, "MAP_mm", "trapmf", [ 100 120 200 200], 'Name', "High");

% Input variable "HOU"

fis = addInput(fis, [0 200], 'Name', 'HOU_ml-hr');

fis = addMF(fis, "HOU_ml-hr", "trapmf", [ 0 0 30 40], 'Name', "Low");

fis = addMF(fis, "HOU_ml-hr", "trapmf", [ 30 40 100 125], 'Name', "Normal");

fis = addMF(fis, "HOU_ml-hr", "trapmf", [ 100 125 200 200], 'Name', "High");

% Output variable "IFR"

fis = addOutput(fis, [0 2000], 'Name', 'IFR_ml-hr');

fis = addMF(fis, "IFR_ml-hr", "trapmf", [ 0 0 60 100], 'Name', "Low");

fis = addMF(fis, "IFR_ml-hr", "trapmf", [ 0 100 200 400], 'Name', "Maintain");

fis = addMF(fis, "IFR_ml-hr", "trapmf", [ 200 400 600 800], 'Name', "Moderate");

fis = addMF(fis, "IFR_ml-hr", "trapmf", [ 600 800 1000 1500], 'Name', "High");

fis = addMF(fis, "IFR_ml-hr", "trapmf", [1000 1500 2000 2000], 'Name', "Very_High");

% Create Rules for the FIS

% r1 = "If HOU_ml-hr==Low & MAP_mm==Low => IFR_ml-hr==Very_High";

% r2 = "If HOU_ml-hr==Normal & MAP_mm==Low => IFR_ml-hr==High";

% r3 = "If HOU_ml-hr==High & MAP_mm==Low => IFR_ml-hr==Moderate";

% r4 = "If HOU_ml-hr==Low & MAP_mm==Normal => IFR_ml-hr==Moderate";

% r5 = "If HOU_ml-hr==Low & MAP_mm==High => IFR_ml-hr==Low";

% r6 = "If HOU_ml-hr==Normal & MAP_mm==Normal => IFR_ml-hr==Maintain";

% r7 = "If HOU_ml-hr==Normal & MAP_mm==High => IFR_ml-hr==Low";

% r8 = "If HOU_ml-hr==High & MAP_mm==Normal => IFR_ml-hr==Maintain";

% r9 = "If HOU_ml-hr==High & MAP_mm==High => IFR_ml-hr==Low";

r1 = "HOU_ml-hr==Low & MAP_mm==Low => IFR_ml-hr==Very_High";

r2 = "HOU_ml-hr==Normal & MAP_mm==Low => IFR_ml-hr==High";

r3 = "HOU_ml-hr==High & MAP_mm==Low => IFR_ml-hr==Moderate";

r4 = "HOU_ml-hr==Low & MAP_mm==Normal => IFR_ml-hr==Moderate";

r5 = "HOU_ml-hr==Low & MAP_mm==High => IFR_ml-hr==Low";

r6 = "HOU_ml-hr==Normal & MAP_mm==Normal => IFR_ml-hr==Maintain";

r7 = "HOU_ml-hr==Normal & MAP_mm==High => IFR_ml-hr==Low";

r8 = "HOU_ml-hr==High & MAP_mm==Normal => IFR_ml-hr==Maintain";

r9 = "HOU_ml-hr==High & MAP_mm==High => IFR_ml-hr==Low";

all = [r1 r2 r3 r4 r5 r6 r7 r8 r9];

fis = addRule(fis, all);

% Evaluate the FIS for inputs [MAP HOU]

% sampleInput = [110 120; 60 25; 30 150; 180 90];

% out = evalfis(fis, sampleInput);

% Plot membership functions

figure

subplot(3,1,1)

plotmf(fis, 'input', 1)

ax1 = gca;

delete(findall(ax1, 'type', 'text'))

text( 25, 1.2, 'Low');

text( 77, 1.2, 'Normal');

text(155, 1.2, 'High');

ylim([-0.2, 1.4])

ylabel({'$\mu$'}, 'interpreter', 'latex')

xlabel({'MAP / mm'}, 'interpreter', 'latex')

subplot(3,1,2)

plotmf(fis, 'input', 2)

ax2 = gca;

delete(findall(ax2, 'type', 'text'))

text( 10, 1.2, 'Low');

text( 60, 1.2, 'Normal');

text(155, 1.2, 'High');

ylim([-0.2, 1.4])

ylabel({'$\mu$'}, 'interpreter', 'latex')

xlabel({'HOU / ml-hr'}, 'interpreter', 'latex')

subplot(3,1,3)

% plotmf(fis, 'output', 3) % there is no Output number 3

plotmf(fis, 'output', 1)

ax3 = gca;

delete(findall(ax3, 'type', 'text'))

text( 0, 1.2, 'Low');

text( 40, 0.8, 'Maintain');

text( 365, 1.2, 'Moderate');

text( 830, 0.8, 'High');

text(1600, 1.2, 'Very High');

ylim([-0.2, 1.4])

ylabel({'$\mu$'}, 'interpreter', 'latex')

xlabel({'IFR / ml-hr'}, 'interpreter', 'latex')

sgtitle("Membership functions for MAP, HOU, and IFR", 'fontsize', 12)

●

figure

opt = gensurfOptions('NumGridPoints', 51);

gensurf(fis, opt);

ax4 = gca;

delete(findall(ax4, 'type', 'text'))

xlabel({'MAP / mm'}, 'interpreter', 'latex')

ylabel({'HOU / ml-hr'}, 'interpreter', 'latex')

zlabel({'IFR / ml-hr'}, 'interpreter', 'latex')

[az, el] = view()

az = -37.5000

el = 30

view(az+180, el)

title("Surface of Human Decision for IFR")

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Michael 26 minutes ago

Love this answer! I ended up just using a generic scatter plot. As for my previous error, "Access violation - no RTTI data!", it was just Mathworks problem. I had to install updates and restart then the error went away. Thank you for the help!

Walter Roberson about 4 hours ago

Good catch!

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Answer 3

Michael about 16 hours ago

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Moved: Walter Roberson about 4 hours ago

"Access violation - no RTTI data!", it was just Mathworks problem. I had to install updates and restart then the error went away.

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