At UCSB, you cannot TAG to Math and then add CS as a major after matriculating as a Transfer.
Students admitted to UCSB as a transfer student are only permitted to major in a College of Engineering major if they were directly admitted into that specific major when they matriculated as a transfer student. Transfer students may NOT petition to change or to add an engineering major, and therefore are not eligible for the CS change of major application process.
For UCI and UCD, it looks possible to double major in Math and CS but not guaranteed.
The Computer Science program is impacted, meaning that there are more students in our majors, minors, or who want to take our classes than there are spaces available. This makes it harder to get classes and transfer into our department than in non-impacted majors. We, therefore, encourage you to use the Internship and Career Center for exploring interests, majors, and career areas to make an informed decision about the major that is right for you, so you can create an interdisciplinary skill set for your future endeavors. Pursuing a CS major will likely result in an extended time to degree.
UCSC information for Double major:
To declare a double major or major/minor program, declare your first major (if it’s not already declared) through the process listed here. Once your first major is approved and declared, add your second major or minor using the process on the same page. Be sure to let your advisors know that you’re planning a double major or major/ minor program! You must file a quarter-by-quarter academic plan showing that you are able to complete the program within the maximum number of quarters of enrollment available to you at UCSC. Students who enter as junior transfer students are expected to complete their degree requirements in two years of enrollment (and are allowed a maximum of three years.