Is it plagiarism if you combine different algorithms to form one algorithm? Im doing a paper where i use a system to combine rules and algorithms from different studies to form a complete program. The ideas were combined and i made a program from that combined idea, now th program itself was made by me and I used solutions which are not exactly the same such as using shortcuts and other functions in matlab. The original papers were all in 1980s, and i was wondering if it is plagiarism to use their algorithms. In my methodology i explained thoroughly their method.
Combining various things to form one new thing is valid research. If your algorithm is a hybrid of 2 others, you need of course to mention these 2 and their authors as well (which you seem to indicate that you are doing). Otherwise you risk your readers thinking that everything in the hybrid algorithm is new, especially since they were developed way back. 
Long story short, if you're acknowledging the work you are basing your approach on, you're being a good student. No plagiarism there.