# Matlab Coder fails generation for slerp() call with double quaternions

3 views (last 30 days)
Kunal Patel on 30 Oct 2020
Commented: Kunal Patel on 9 Nov 2020
I am using MATLAB coder to generate code for following function.
function [D] = getInterpolatedTransforms(q0,t0,q1,t1,steps,correction)
D = zeros(4,4,steps);
for i = 0:1:steps-1
coeff = single(i/steps);
qt = slerp(q0,q1,coeff);
tt = [t0*(1-coeff)+t1*coeff,1]';
D(1:3,1:3,i+1) = (quat2rotm(qt))*correction;
D(1:4,4,i+1) = tt;
end
end
I get following error while generating code at the "check for issues" step
??? This assignment writes a 'single' value into a 'double' type. Code generation does
not support changing types through assignment. Check preceding assignments or input
type specifications for type mismatches.
Error in ==>> quaternioncg Line: 48 Column: 17
Code generation failed: View Error Report
??? This assignment writes a 'single' value into a 'double' type. Code generation does
not support changing types through assignment. Check preceding assignments or input
type specifications for type mismatches.
Error in ==>> quaternioncg Line: 48 Column: 17
Code generation failed: View Error Report
The location of the error is in Matlab internal file quaternioncg.m
James Tursa on 2 Nov 2020
Maybe you could tell us which line is generating the error?
Could you use double types instead? E.g.,
coeff = double(i/steps);

Darshan Ramakant Bhat on 2 Nov 2020
Solution 1 : Remove the single cast
function [D] = getInterpolatedTransforms(q0,t0,q1,t1,steps,correction)
D = zeros(4,4,steps);
for i = 0:1:steps-1
coeff = i/steps;
qt = slerp(q0,q1,coeff);
tt = [t0*(1-coeff)+t1*coeff,1]';
D(1:3,1:3,i+1) = (quat2rotm(qt))*correction;
D(1:4,4,i+1) = tt;
end
end
Solution 2: Make the input quaternion as single
>> a = quaternion(single([45,0,0]),'eulerd','ZYX','frame');
>> c = quaternion(single([-45,0,0]),'eulerd','ZYX','frame');
>> codegen getInterpolatedTransforms -args {a,1:3,c,3:5,10,0.5} -report
Kunal Patel on 9 Nov 2020
Thank you, This worked.

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